Thank you very much for the responses. It sounds like getting it checked by an independent dealer for a second opinion is a sensible next step. To respond to some of the specific points:
The leak isn't severe at all as far as I can tell. Certainly no signs of oil externally or in or around the engine. I should have mentioned that they also said there was a rocker cover leak, but the price they quoted to fix that was reasonable (as in 3 figures..) so I didn't think too much else of it, but equally the lack of sign of oil in the engine bay does make me wonder about that one too. I will probably speak to Audi again and ask them how exactly they identified these leaks and how serious they perceive them to be. I don't know if they are just recommending this more as a preventative maintenance item than anything else.
Fair question, although to my mind 6 years isn't exactly old. I guess I still cling to the notion that main dealer service history is important for resale value, although of course I know there are different schools of thought on that.
Yes I am now too! I haven't been underneath the car myself no and I don't have access to a lift or anything, but I will speak to Audi again and see if I can get any more insight. Interestingly they sent me a video of the car on the ramp during the inspection, and in the video they didn't look under the engine or otherwise show any signs of a leak either.
I was certainly planning to keep it for a few years, but that could easily change because frankly I'd sooner sell the car than pay this kind of money to fix an oil leak!
Thanks for the recommendation but I am based in Ireland, and we don't have too many highly regarded VAG specialists that I am aware of!