I know you can change a 2004 CL 600 from air to hydraulic spring suspension,the reason MB came away from the ABC system was that material flaking away from inside the pipes block and wreck the ABC,and then you get mechanics flushing the system charging a fortune and after a short while the system goes down again because you have to replace all the pipes and the pump,flushing does not remove all the debris,and so we got air suspension,posters are right the ABC system is better than air,it is just that it is a high cost system to maintain,but the cost has gone down alot in the past few years as companies have focus on the niche of supplying pumps and pipes cheaply