Nightowl, i've just been through this process.
My suspension was dropping overnight and the compressor was working hard to get it up to level when driving. We diagnosed leaking struts on both front sides. I'd looked at various options including Aerosus and also replacing the bags. TBH, the latter felt like a cheap out, short term option so I went with RMT based out of Florida.
https://rebuildmastertech.com/audi/a...rt-suspension/
They offered me two rebuilt cores for a total of USD$589. The deal is that you pay a deposit of USD$300 for cores and they refund this to you when you return yours back to them. Obviously you can decide not to return them and your other option is to remove yours and send to them.
It took them a day to source the cores and from placing the order to receiving a shipping advice note it took 5 days.
They're currently being fitted as I write. I'll let you know here if there's anything untoward but overall my experience with RMT was excellent.....
I've also taken the opportunity to replace all of the suspension arms with TRW parts so looking forward to seeing how it ends up ride wise.