High mileage A6's. Issues, problems?

[warp9]

Hi. I'm after an A6 Avant, have around £12K to play around with and would like something that's a bit pokey with the Quattro system. That has pretty much led me to 3.0TDI's. However most of them have well over 100k miles on the clock. Is this an issue, what am I looking out for and are there any known issues?

There also seem to be a lot of Allroad variants out there. I don't really need the extra clearance, can it be lowered and are there any other differences to consider.

High mileage example (although not derv) http://www.pistonheads.com/classifieds/used-cars/a...

Cheers

[warp9]

Dr G, really useful post, thanks for that.