Jim,

I had this same problem a month ago on my '91 560 SEL (101K miles). Accumulators were deemed fine, but the rear shocks were shot. If you rode in the back, it was bone jarring. I had OEM replacement shocks installed (Bilstein) and all is well. An expensive part, from the dealer around $370, but you can find them $100 cheaper from
Rear seat had to be removed -- so there is at least 3 hrs. labor invloved (I had the hydraulic system bled and new skins put on.)

Hope this helps,