I would be looking for possible leaks now, especially since you found the system to be 2 liters low. That fluid has to be going somewhere. Could two bad cells hold 2 liters of fluid????

I don't know how to specifically test the pump, but you could check leveling function by crawling under the car at the rear, look just right of the differential, you should see the valve. Disconnect the linkage (takes a 10mm open and a 9mm {Ithink, might be an 8}open to counter. Loosen the nut and remove one end of the linkage. Now with the engine running, pull the lever down about an inch, if working the rear should lift. If the direction of movement of lever is wrong, I reckon the back will lower.

The nitrogen cells will be in this same area, mounted up on the underside of the body near the shocks. Can't miss them - the size of a softball and black.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.