ddkilburn

My 2012 W251 randomly drops overnight, a couple of times a week. I believe it starts in the right rear but the difference is subtle and am not sure. All four corners drop, rear more pronounced. Seems random. Car can be parked for a week and be fine, go out for a short drive and the next morning it's on the ground. Unlock the car, compressor starts up rises to drive height. Difficult to replicate at the shop because it is occasional.
This is what i've had done:
- tested valves, lines and connectors, no leaks found
- replaced all 4 sensors, replaced right rear again
- replaced airmatic valve block
Any ideas about what to have them check next?
Many thanks
2012 R350 BT , 178K km
Many thanks