If you're getting what seems like rear-end steering when the gas is applied (or let off), it's highly likely that it's the rear links that are worn. More specifically, the diagonal thrust link (although it's possible the others are worn too). It is supposed to hold the wheel straight ahead when torque is applied to it. It was eventually updated with a stronger part from the W210.

You should look at all the other items mentioned previously, since the rubber bushings used all over the suspension degrade with both use and time, but the thrust link is probably a good place to start.