All generations and engines together · 26,702 MOT tests in the 2025 data · typical mileage at age 7: 27k
Worse than most coupés and convertibles per mile driven. Watch brakes and suspension. A used buy worth some caution. Check the MOT history for repeating brakes advisories before you go.
Split by first-registration year. Cars registered in a changeover year can belong to either generation.
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.
On the M272 and M273 V6 engines (SLK280, 300, 350, 500 of the R171 era, roughly 2004-2011) the balance-shaft sprocket is made from a metal that's too soft and wears down, letting the timing chain jump and knock the engine's timing out. Early signs are a rattly, chattering noise from the front of the engine and a check-engine light, usually somewhere past 60,000 miles. Mercedes never recalled it in the UK but it was significant enough to trigger a US class-action settlement, and a full repair with genuine parts runs well into four figures.
The vario-roof is the SLK's signature party trick and its biggest headache. Rubber microswitches harden and stick if the car sits unused, hydraulic ram seals weep and lose pressure, and the roof motors themselves can seize, leaving the roof stuck half open or half shut with the boot lid flapping. It happens across all three generations, though the R171 moved the hydraulics into the roof itself rather than a remote ram in the boot, and the R172 is generally better sealed. A full roof strip-down and motor or ram replacement is not a cheap job.
Owners regularly complain that front discs and pads on the SLK don't last as long as they'd expect for the mileage, and that a Mercedes dealer quote for genuine discs and pads can run to several hundred pounds a side. The measured MOT data backs this up directly: brakes are the standout fault category for this class of coupe, so what owners are grumbling about on forums is the same thing showing up as advisories and fails at test time. Branded aftermarket discs and pads (Ferodo, Mintex) are a common and much cheaper workaround.
On the V6 SLK320 (and reported on later 350s too) the right-hand pre-cat and main catalytic converter are known to fail prematurely, often flagged by a check-engine light, a rattle inside the exhaust, or a drop in performance. Honest John notes Mercedes itself was quoting around £1,400 for the pair when new, so expect a similar or higher bill on a used one now. It's a V6-specific issue, not something four-cylinder SLKs are reported to suffer from.
A recurring complaint across SLK generations is the air-con compressor packing up, usually announced by warm air from the vents, a clutch rattle from the compressor pulley, or the compressor seizing outright. Honest John has flagged replacement costs around £1,600 at a dealer, though independent specialists and reconditioned units bring that down a long way. There's no TSB or recall for it, just a steady stream of owner reports.
Some R172-generation cars (built 2011-2016) have shown fine paint blistering across body panels, not just stone-chip damage at the edges but a general pinprick texture in the clearcoat. It's cosmetic rather than mechanical, but it affects resale value and a respray to fix it properly isn't cheap. Not reported on the earlier R170 or R171 cars.
Ranked from this model’s own MOT record, then from what owners report.
Saveable checklistThe physical checks its own defect data says are worth your time, most telling first.
These judge the seller’s upkeep rather than the model, and they are where the haggling money is.
The physical checks its own defect data says are worth your time, most telling first.
These judge the seller’s upkeep rather than the model, and they are where the haggling money is.
The physical checks its own defect data says are worth your time, most telling first.
These judge the seller’s upkeep rather than the model, and they are where the haggling money is.
Drawn from the reports above rather than the MOT data. These are the model-specific ones.
Computed from DVSA MOT results, all of Great Britain, 2025. Nothing here is opinion.
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.
The rows that judge the model rather than its keeper. 3,631 tests in this band.
Tyres, pads and stone chips say more about how the car was driven and maintained than about how it was built.
Same segment (Coupés, convertibles & GT), best MOT record first. Compare before you shortlist.