As stated a careful check of all rubber is important. Also, check tire pressure amazing the difference five or six psi makes. I find that all tire shops set the tires at 40+ psi for seating of the bead but do not lower to spec afterwards.

Does your car have SLS? It may have been optional on some W126 cars, standard on 560's. Then the culprit would be the accumulators. Shows up as a nervous and harsh ride quality much as you describe.