Hi Dan
I believe all the airbags are independant.
However my front left bag has a leak more so on level 1 or 2 you can clearly hear it hissing, when the car ignition is off it starts sinking on that side, this lowering must trigger the level sensors so the other 3 wheels lower. As the airbags lower by one level and then again until they are on the lowest level, and the leaking one, the wheel is right in the wheel arch, (lower than the rest). They are all independant so one leaking should not alter any others appart from, when off, showing perhaps this lowering symptom to try and keep the car level.
The rear sticking up in the air is strange and would point to the Compresser module which has the air release valves to lower the car, but this is just a guess or start point, if the compressor has been running constantly to pump air, it will do itself damage and perhaps the valves also,
The compressor is under the car in front of the spare wheel well.
i have been trying not to run the car and if i do keep it in level 3 as it only leaks slowly in that level.
the Air bag i have ordered is from:
http://www.arnottindustries.com/part...17_pid124.html
its around £250 with supposed lifetime warranty but i have seen forums mentioning they are OK.
My Local Audi wanted £400 so i took my chances with Arnott, they also do rear units and coil overs to completely replace the airbag units, not for me but i can see the idea.
Delivery to the UK is around 2 weeks so i hope to get it fitted when it arrives
hope you solve yours economically as you can
i will let you know if it stops the car sinking when i fit it, it better!!
regards
Andy