Yeah, your right, On my 2002 C240 there is a black plug topped tube, that allows one to use the suction method of withdrawling oil from the sump.
That is for engine oil. It is shown in the owners manual, that I downloaded.

I cannot remember if there is a trans dip stick tube back there or not.

On the 2002 the engine cover is two part, front cover covers power steering reservior, but the rear does pull up and it has the two intake tubes that get pulled from their anchor near the front cross brace. 2003 E class may be different.

Sorry about that