Hi Skiduk
I’ve got the same A6 model, had it 3 years now and still love it ,
Ive used Derby Audi for servicing which has been under Audis All in service plan.
My front brakes pad are down to 70% wear and Audi have just quoted me £1050 just for front discs and pads, I’m going to do them myself and have managed to get the parts for £350 .
Rear spring mount rubber’s corroding was an mot advisory when the car was 4 years old, Audi quited me £320 each side for replacing them but did them myself rubber mount were £50 ,
Tyres Continental x4 £860 .
My A6 has had 2 faults in the it’s 5 years which were both rear door locks playing up and they were replaced and a brake servo restriction fault ! That was a little pressure switch near the servo that monitors vacuum, both fault were repaired under the all in warranty . I don’t think it’s been bad at all personally
Hope this helps mate