My 2011 ML550 was spewing oil all over the passenger side engine, burning on the manifold, etc. Wasn't
the oil separator as is usually suspected, not valve cover gaskets...because there are none. Turns out
there was a hairline crack in the oil filler cap that only leaked under pressure - doesn't happen when just idling....

Just an FYI to check it first if you have this mysterious nuisance...is very tough to spot in the wild!

 

Thanks for reporting that back.