2006 E53 4.8is Self Leveling Suspension issues and codes

[cmbenedict]

I know this is an extremely common topic but I can't seem to find enough info in other threads to know what to do next. Please let me know if you need additional information.

Self Leveling Suspension issues in past (2016) resolved by installing piston rebuild kit by bagpipingandy. Came back recently so I figured installing a new kit would resolve but no luck. Every time I take X to tech he clears code and compressor comes back on. A day or two later fault reappears. After 6 trips to reset I bought PA Soft to be able to reset myself until I figured it out.

The good news is that the airbags must be in good shape as the vehicle doesn't sag even after 2 weeks in cold weather so the problem must be elsewhere. I checked the connections in the rear and no obvious leaks/hissing. Ran PA Soft again today to reset and came up with following codes/error messages:

1) Under Light Check Module, I get a shadow code of 57[087] Level control system (not sure if this means anything but included anyway)

2) EHC -> 74/68 - Reservoir pressure remains constant, when filling of reservoir is requested
09/24 - Reservoir-valve

3) ABS* -> 60AF/A0 - RPA-Error: detection deflation system: RPA inactive, difference of the level of the front axle_air suspension is to big
60B0/A0 - RPA-Error: detection deflation system: RPA inactive, difference of the level of the rear axle_air suspension is to big

Other pertinent info:
- Vehicle sits at correct height - at least visually
- the system does not appear to be leaking. Doesn't sag with pump fault for weeks at a time
- When I clear fault and the compressor runs I can't change the ride height in either direction (can't raise or lower vehicle) yet green indicator lights are on and will flash.

It seems that when the compressor kicks on the pressure tank is either not getting fed or is not recognizing the increased pressure. Not sure how to interpret the errors listed above. What is the "reservoir valve?" Any ideas on what I should be looking for? Bad sensor? Clogged line?

Thanks in advance.