Well, to update on my 1985 380SE, with nearly 270K, I still have no actual squeaks or rattles, but the door panels "scrunch" like crazy, even on smooth roads... they "scrunch" with road motions. The seats may be part of it, but they are MB-Tex and still are soft, so I do not think so.

I am guessing this could classify as squeaks (the door panel scrunching)???
Also, since someone had installed a hard plastic dash cover, over the cracked original one, it will "scrunch" as well over bumps.