I found an excellent source of information on maintaining the
suspension of my 1990 300TE. Also relevant for 560 SEL/SEC cars.
Register with them, then search the forums for:
"hydraulic suspension" or "suspension fluid" - great info on how to
perform fluid change, and save yourself some $$$ and hassle using the
methods they talk about
"accumulators" - great info on how to replace accumulators, where they
are in the car, etc.