Fault File
All models / All cars / Coupés, convertibles & GT / Mercedes SLC

Mercedes SLC

All generations and engines together · 8,967 MOT tests in the 2025 data · typical mileage at age 7: 37k

Reliability verdict
CBy age
EBy miles

Graded against its peers

Middling for its age among coupés and convertibles, but one of the worst per mile driven. Watch suspension and wheels. One to judge on its mileage rather than its age, and worth it only if its MOT history has no repeating suspension advisories.

First-time failure at age 7
15.9%
Across 2,473 tests. The average for coupés and convertibles is 14.8%.
First-time failure at 50-60k miles
23.9%
Across 821 tests. The average for coupés and convertibles is 17.9%.
Rank in its class
14 of 19
1 = lowest failure rate among the 19 coupés and convertibles we can rank.
Typical mileage at age 7
37k miles
How far the average car has gone by seven years old. Low-mileage models can look better by age than they are.

What owners report

Reported

Owner folklore from forums and the motoring press, with how well each report stands up. Most of it never shows up in an MOT, which is why this section exists at all.

Folding hardtop leaks and delamination

Confirmed pattern

The metal folding roof's headlining or seal can come unstuck, most often at the front edge, letting water through onto the passenger's lap in heavy rain. Owners on Mercedes forums describe it worsening over a year even after a specialist re-bonds it, and Mercedes itself has treated leaking as a known issue rather than a one-off. It tends to show from around 5 years old and a re-bond or roof panel replacement runs into four figures.

Reported from ~5 years old, repairs roughly £1,000-£4,000 · sources: MBClub UK forum, HoodTech roof diagnostics

Roof mechanism sticking or stalling mid-cycle

Emerging

Separate from the leak, the powered roof can jam partway through opening or closing, or the front catch can refuse to release, usually down to worn microswitches, a weak roof pump or a stretched drive cable rather than anything structural. It is a known nuisance fault across R172-generation folding hardtops (SLK and SLC share the mechanism) and shows at any age once components wear. A specialist diagnosis and repair is normally a few hundred pounds unless a motor or ram needs replacing.

Any age, repairs from a few hundred pounds · sources: HoodTech roof diagnostics, MBClub UK / SLK World forums

Front suspension knocks and clonks

Partly in the MOT data

A recurring complaint on the R172 platform is a clonk or knock from the front end over bumps or on lock, usually traced to worn front strut top mounts, anti-roll bar drop links, or (on AMG models) Airmatic strut wear. Forum regulars treat a slight knock as a known, fairly common fault rather than an emergency, but left long enough the links and bushes will fail an MOT. The measured MOT data for this model does show suspension as the standout failure category, which lines up with the forum chatter about clunky front ends, though the data can't say whether it's the strut mounts, drop links or something else in the chain.

Reported from ~50k miles, drop links/bushes typically £150-£400 · sources: MBClub UK forum ("knocking suspension" thread), BenzWorld forum

M274 2.0 turbo thermostat and camshaft actuator faults

Emerging

The four-cylinder M274 turbo used in the SLC 200/300 can suffer a seized or failed thermostat housing, which stops the engine reaching temperature and can trigger cooling warnings, and worn camshaft actuators that throw fault codes and rough running. Neither is usually terminal but both need attention, with thermostat housing replacement typically a few hundred pounds. This engine is shared across several current Mercedes models so the failure pattern is well documented outside the SLC specifically, not unique to it.

Reported from ~60-80k miles, thermostat housing repair roughly £300-£600 · sources: Mercedes specialist diagnostic write-ups (mercedesdiagnostics.com, mercedesassistance.com)

Electrical gremlins in sat-nav and minor controls

Emerging

What Car's reliability coverage notes that reported problems on the SLC are generally few, but where they do crop up it's usually electrical gremlins affecting the sat-nav or minor switchgear rather than anything mechanical. These tend to be intermittent and can be fiddly to pin down, sometimes needing a software update or a connector reseated rather than a big repair. Not a big-ticket item on its own, but worth flagging as the most commonly reported niggle.

Any age · sources: What Car used SLC reliability review

What to check on this car

Ranked from this model’s own MOT record, then from what owners report.

Saveable checklist

From this model’s MOT record

The physical checks its own defect data says are worth your time, most telling first.

Wheel bearingsRuns high on this model On the test drive, listen for a drone that rises with road speed and shifts when you sway the car gently between lanes. That is a wheel bearing, and it only ever gets louder.Recorded on 3.8% of tests at age 6-9 · class average 0.5%
Coil springsRuns high on this model Look through the wheel spokes at the bottom coil of each spring; when springs snap it is usually there, and the break is visible. Step back and check the car sits level too. A dropped corner is often a broken spring.Recorded on 2.5% of tests at age 6-9 · class average 1.4%
WheelsRuns high on this model Look at each rim for kerb damage and check no wheel nuts are missing. A steering wheel that shimmies between 50 and 60 on the test drive often turns out to be a buckled or badly balanced wheel.Recorded on 2.0% of tests at age 6-9 · class average 0.6%
Rubber boots and gaitersRuns high on this model On full steering lock, look in behind each front wheel at the concertina rubber boots on the driveshafts and steering rack. Splits, or grease flung around the arch, mean dirt is getting into a joint that costs far more than the boot protecting it.Recorded on 1.7% of tests at age 6-9 · class average 1.0%
Bushes and ball jointsRuns high on this model Drive slowly over broken tarmac with the windows down and listen for clonks from either end. Back at the car, have someone rock the steering wheel while you rest a hand on each front wheel; play you can feel through the tyre is a worn joint.Recorded on 1.7% of tests at age 6-9 · class average 0.7%
Dampers Look for oil misting on the damper body behind each wheel, then push down hard on each corner of the car. It should settle in one bounce. A floaty or crashy ride on the test drive is the same fault felt from the driver's seat.Recorded on 1.0% of tests at age 6-9 · class average 2.3%
Warning lights on ignition Turn the ignition on without starting the engine and watch the dash. Every warning light should appear, then go out once it is running. Be more suspicious of a light that never comes on at all than of one that stays on; warning bulbs have been known to vanish before a sale.Recorded on 0.8% of tests at age 6-9 · class average 0.3%

Worth doing on any used car

These judge the seller’s upkeep rather than the model, and they are where the haggling money is.

Tyres, all four Check the tread across the full width of each tyre, inner edge included, and look for cracking and mismatched brands. A set of decent tyres is £500 or more on most cars, which makes this the easiest money to take off a price. If the pressure warning light is on, budget for sensors too.Recorded on 22.9% of tests at age 6-9 · class average 20.1%
Pads and discs Look through the wheel spokes at the brake disc. A pronounced lip on its outer edge, or a rusty and scored face, means discs and pads are due all round, a few hundred pounds on most cars. A haggling point rather than a reason to walk away.Recorded on 5.7% of tests at age 6-9 · class average 10.1%
Windscreen and wipers Scan the glass in daylight for chips, especially in the driver's line of sight where even a small one can fail the MOT. Run the washers and check the wipers clear without smearing.Recorded on 1.6% of tests at age 6-9 · class average 2.0%

Because of what owners report

Drawn from the reports above rather than the MOT data. These are the model-specific ones.

Run the roof through a full open/close cycle at least twice. Any hesitation, stalling partway, or the front catch not releasing cleanly points to the roof mechanism fault.
With the roof up, check the headlining edges and door seals for damp patches or watermarks, and if it's rained recently, feel the front footwells and seat base. Damp carpets or a musty smell means the roof has been leaking, whether or not it's been re-bonded since.
Drive over a rough patch of road and turn the wheel lock to lock at low speed in a car park. A knock or clonk from the front end suggests worn strut top mounts, drop links or bushes, the fault that shows up as the car's most common MOT failure.
Check the coolant level and look for any recent cooling-system warnings in the service history. Repeated coolant top-ups or a warning light history hints at the M274 thermostat housing fault.
If it's a 250d diesel, ask for a hard motorway run and watch for any power reduction or limp-mode warning. Sudden power loss points to an EGR, DPF or injector problem on the OM651 engine.
Cycle through the sat-nav menus and every switch on the dash and doors. Freezing screens or dead switches are the electrical gremlins owners report most often.
Pull the full MOT history and look for repeat suspension advisories. The same advisory two or three years running means the knock has been ignored, not fixed.

Open the saveable checklist, tick it off at the car

The MOT data

Measured

Computed from DVSA MOT results, all of Great Britain, 2025. Nothing here is opinion.

How this model wears

Mercedes SLCClass average, all tracked models

What testers flag

Share of tests where each item was recorded. The dark tick is the class average across all tracked models; bars are scaled within each group.

Faults with the car itself

The rows that judge the model rather than its keeper. 7,568 tests in this band.

A wheel bearing with excessive play
Advisory
3.8%class 0.5%
A suspension joint dust cover severely deteriorated
Minor
2.5%class 1.1%
A spring or spring component fractured or seriously weakened
Fail
2.5%class 1.4%
A wheel badly distorted or wear between wheel and hub at spigot mounting
Advisory
2.0%class 0.6%
A suspension pin, bush or joint excessively worn
Advisory
2.0%class 6.7%
A suspension joint dust cover missing or no longer prevents the ingress of dirt etc
Fail
1.7%class 0.9%
A suspension pin, bush or joint excessively worn
Fail
1.7%class 0.7%
A shock absorber damaged to the extent that it does not function or showing signs of severe leakage
Advisory
1.0%class 2.3%
Warning device shows system malfunction
Fail
0.8%class 0.3%
Engine MIL illuminated indicating a malfunction
Fail
0.7%class 0.5%

Wear, upkeep and luck

Tyres, pads and stone chips say more about how the car was driven and maintained than about how it was built.

Tyre tread depth not in accordance with the requirements
Advisory
26.1%class 22.9%
A tyre seriously damaged
Advisory
18.6%class 13.4%
Brake disc or drum excessively weakened, insecure or fractured
Advisory
5.7%class 10.1%
A brake lining or pad worn below 1.5mm
Advisory
3.5%class 8.7%
A tyre cords visible or damaged
Fail
3.1%class 1.2%
A tyre seriously damaged
Fail
3.0%class 1.8%
Brake disc or drum significantly and obviously worn
Advisory
2.8%class 3.4%
Tyre tread depth not in accordance with the requirements
Fail
2.0%class 2.3%

Others in its class

Same segment (Coupés, convertibles & GT), best MOT record first. Compare before you shortlist.

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