MB hydro suspension has a habit of eating nitrogen spheres on high mile cars. This is especialy true if anything other than the original fluid has ever been added. This system simply won't tolerate anything else. If your suspension has very little travel and appears to be very firm I'd say you need spheres. If you would have a mechanic from a quality independent shop, i.e. a Bosch Service Center,take a quick test drive you probably would get a free confirmation of this diagnosis. Most MB dealers look down their noses at grey market cars. Frankly this is their loss.