Yes, I would also check ride height as suggested by David. W140s have extremely good and forgiving ride, even if the shocks are not up the standard.

The real problem comes from the rear self-levelling suspension or the full hydraulic setup. When either system starts giving trouble, that is where the ride start to suffers, and badly. So I would basically asume there is a problem with something on your rear axle, it is just a matter of taking the time to find out what it is.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]