My passenger rear was sagging a few weeks ago so I removed the rear valve block, cleaned it, replaced the orings and reinstalled a spare valve block I had on the shelf. I also flushed the system, new fluid and a new 3 micron filter installed. There were no leaking or weeping hoses or struts, everything was bone dry.
Anyways, the rear still sagged so I reinstalled the original valve block that I had rebuilt but again no difference and no leaks. So the rear sags on one side with either of the rebuilt valve blocks and I have no leaks, clean fluid and new filter. The only thing I can think of is the strut itself bleeding down internally? I reused the same accumulator sphere but I figured if it was bad both sides would sag? Has anyone ever seen a strut with an internal leak? Can it be rebuilt like the valve block?

 

You may want to post in the S55 forum. The 211 E55 has airmatic.