I don't think you'll get any Audi main dealer to do this - I didn't, and like others on here, I'd point you in the direction of either Mackies (Glasgow), or Chester Transmissions (Chester, unsurprisingly…
).
Links are here:
http://www.mackie-transmission.com
http://www.transcentre.co.uk (I think…)
Service cost at Mackies is £155, more than that at Chester Auto (£c.250 from memory…).
There's also a couple of longish threads on this, here's one which covers the box replacement (which hopefully is less relevant to you..
…)
http://forum.a8parts.co.uk/showthread.php?t=5719