Have you had the fluids checked at the dealer after you got the car. It has hight mileage correct, even thou the tranny is supposed to be sealed for life, most people with these tranny change the fluid at 100K miles some at 50K, also the rear differential could be the source, or the CV joints in the rear, there are a lot of possibilities. check to see if any booth on the rear axle are cracked. Perhaps the grease is gone? Also could be a sticking, now and then caliper. Lots of stuff to go thru. I would take it to an MB shop or dealer quickly especially if it is the tranny.

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Al Lueb
1999 C280 54K miles
1979 450 SLC 144K miles