If it's a US spec S500 then it has the self leveling feature. The struts don't normally go bad. Lots of times replacing the nitrogen cells will restore the ride.

What worries me about your question is that if you don't know that your car has leveling suspension, has someone been changing the hydraulic fluid and filter per the recommended schedule?

Sixto
95 S420
91 300SE
87 300SDL
83 300SD