2001 allroad, rear suspension drops overnight

[skyegtb]

Hello all, sorry for yet another allroad suspension thread, but I am stumped this time for the first time in the 10 years I have owned the car!

When left sitting overnight, whether at level 1, 2, 3, or 4, OR in jacking mode or not the rear of the car will equally drop to the ground on both sides. Every 12 hours the rear will drop by almost exactly 1 level until the rear eventually equally hits the bump stops, yet the front stays fully up.

What have I done so far?
Checked for error codes - NONE.
Checked in great detail with the car on a car lift for any leaking areas at the rear using soapy water - NONE found.
Tried every level and jacking mode in every level overnight and always the same result, both sides equally drop.
I checked in great detal for leaks at the valve block, compressor and all pipework - NONE found.

To be honest, I have lived with the car like this for the last 3 months and I can continue living with it, so long as it does not get a lot worse, BUT I would really like to fix it as it riles me immensely seeing the car dipped down at the rear!

Any assistance would be greatly appreciated. What should I try next?

[amiram]

For starters I would disconnect the battery overnight to make sure it was not caused by the module. if you have a headlight height control system in 2001, this system can also affect an air spring system. Next I would try to figure out if the leak is internal within the system or external. To do this you need to expose the suction and exhaust pipe of the air spring system located in the spare wheel area and connect a children's balloon on it for night.

[Crasher]

So it just sits on its ****?

[amiram]

So it just sits on its ****?

The diagnosis is made in stages and this is the first.