If you own an allroad and you have suspension issue(and you will) first port of call should be a compressor repair. I have just done this and the results are amazing, no more fault light and the levels change in a fraction of the time.
I bought mine from bagpipingandy.
£35 for kit or least £300 for new pump.
The kit comes with instructions new bolts, o-seal and PTFE o-ring.