I'd suggest looking on Audi A6/A7 forums for info as the D4 mechanism looks quite similar in operation. The D3 mechanism is quite different and possibly more complex/over engineered.
There is mention of a D4 A8 on here but very little detail other than most were repaired by Audi under warranty. Let us know how you get on.
http://www.vwaudiforum.co.uk/forum/s...ing-MMI-screen