It's a bit of a pain to get the tailgate trim off the first time. The Haynes manual has a good guide and so does the forums on here. It's a couple of screws 2 of which are by the hazard triangle, 4 metal clips and a special tool to free it from the rest of the trim. Easy once you've done it once before.
As above your motor is probably leaking internally, there are repair kits on eBay but a new one from audi is £80 ish. A doddle to change once the trim and wiper arm are off!
Good luck