This car is a '84 500 SEL that I recently purchased. This car has the Hydraulic leveling system on all four wheels, (no springs) One rear shock is leaking as is the leveling valve in the rear. I purchased those and plan on putting them on the car but I am wondering if I should wait to see if these Hydraulic reservoirs (nitrogen spheres) need changed as well. I heard that when they go bad, the car will act as if it has no absorber. It is almost there now.

Does anybody have any ideas on how to check them before I go out and replace all five for $100-150 a piece? Will this system require any specific bleeding procedure when all that equipment come off.
Thanks,
Bill Hunt