560sec suspension

I own a 1987 560SEC with a loud thud coming from the rear of the car when at low speed the car goes over road bumps. The car has a hydropneumatic self leveling suspension. I was told it could be a number of things, rear shock bushings, bad accumulaters, or the shocks themselves. What can I eliminate as the possible cause or better yet what has not been considered as a possible source. Thanks for any help that can be given!

[Luke@tirerack]

a friend of mine had the same problem and he couldn't figure it out either until we jacked up the car and got under there to inspect everything .... we found that 1 of the shocks had broken a mounting bolt .... drilled out the old bolt put in a new one .... problem gone