i think it runs the same as the e34.
Check the accumulators, those little bomb looking things http://forums.roadfly.com/forums/bmw...6503297-1.html
Check for any leaks around the top of the shocks, and the lines that go to them.
If the same as the e34, they have a dual stage power steering pump that also runs the SLS system. make sure its not leaking, and is filled up. ONLY run Pentosin 7.1. It should be marked on the resevoir
I had the same problem in my M5, When i bought the car it would sag so low, and wouldnt come back. and the car was terrible to drive.
the seals go in the shocks and are virtually impossible to fix, and replacements are expensive. but I had found a used set from a member here.
Your other option is a SLS delete.
hope this helps.