Noobamgdude

Hello,

I bought a 2004 SL55 a month ago and am currently having some preventative maintenance done on it at the shop. The valve cover gaskets were changed by the previous owner 2 years ago but they are starting to weep again so the mechanic opened removed the valve covers and found that both have rot holes straight through at the seams.
The mechanic said that this was probably due to the age of the car. But from all the research I've done before buying this car, it seemed to me that the engine was supposed to be quite bulletproof so I'm wondering about the cause of this.
I'm worried this could be a symptom of a bigger underlying issue so I would be grateful if anyone could shed some light on the potential causes and how I should prevent this from happening again.
Thank you so much

TECHNICIAN

I've seen them rot internally in the PCV area but never externally like that. Likely a symptom of the environment the car was in and/or poor repairs previously done. I wouldn't be concerned after replacement

Dave34653

My 2004 C240 had the same thing which I found when doing my gasket change.I thought maybe some wires were grounding in that area but no wires are around my covers rot.

chassis

These valve covers are likely magnesium. Magnesium is very light, fairly strong but unfortunately very reactive. Rot can be cause by dissimilar metals exposure (iron, steel, aluminum). Or by caustic cleaning solutions sprayed on the engine at some time in the past.

Best solution is to replace the cover with a new one and avoid cleaning the engine with liquid or solvents. Dissimilar metal corrosion can't really be dealt with without replacing all the gaskets and seals in the engine, which is not practical.