Hi. I'm just getting to know my new purchase (1995 C200 in unbelievably good order). In the engine bay I have noted the presence of this yellowish deposit on the engine, inlet manifold and other metal surfaces. It also extends over the plastic cover at the front of the engine. It can be scraped off with a fingernail. I have noticed the same stuff in photos of other Mercedes engine bays on cars of a similar age, but I've never encountered it on other non-MB cars. Is it some sort of Mercedes-applied coating that has gone off over the years? Is it a corrosion product on the alloy of the engine casing? Or is it where someone has used a dubious product to clean the engine bay? Apologies if this is a daft question with an obvious answer!