You’re in a bit of a predicament Nicola. The trouble with main franchise dealers, and this isn’t exclusive to Audi, is that their technicians aren’t experienced enough. As mentioned earlier, if anything like BMW, then they will log onto a computer terminal and follow as prescribed route to fix and don’t use old fashioned intuition. That’s fine if they actually fix it, but as a customer you take the hit with exorbitant labour and parts.
Personally, I’d take the car back from Audi dealer and continue with your route to Audi UK to see if they can address it. This is a luxury SUV, 5 years old, and shouldn’t have something that’s unfixable.
There must be some sort of monitoring system for air suspension that provides live data. The fact the car self levels on start up tells you the compressor is doing its job. I’d want all the self levelling height sensors checked. That should have been done as a matter of course, and with live feed to VCDS to see functionality.
Airbags, as mentioned by John, inspected properly. Whether it’s the airbag, ‘o’ ring or line feed union. Audi won’t repair, I will tell you that now. If there’s a fault then they’ll opt to replace. The air lines traced to see if there’s a break along the length of the car from the compressor. That’s why they want the seats out. I think at that point, then this repair should be goodwill, as stripping out interiors is time intensive.
I gave up on main dealers years ago and do my own work. VCDS is useful, but Audi will use systems such as ODIS with component security protection which is dealer level software that your average mechanic won’t have access to. On the latest Golf MK8, you can’t even change the rear pads without ODIS is my understanding.
Anyway I hope you get a resolution to this.