Yo might check your coil dpring on that side. If you park the car on level ground, is one side lower than the other. I had a broken coil spring on my back end ('86 420SEL) and it made handling lousy, especially in city driving (lots of corners) and it wandered on the highway. A new set of rear springs cured it 100%.
1995 E420 - retired
1986 420SEL - retired