Timing chain tensioner leaks down
M271Commonly on W204-era cars; gets worse, not betterA metallic rattle for a second or two on a cold start, worst after the car has stood overnight.
The hydraulic tensioner does not hold oil once the engine is switched off, so the chain is slack at the moment of start-up. Left alone it fatigues the chain and can eventually jump timing, which turns a tensioner job into an engine job.
Parts this needs
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