Just from my experience...
VAG Diesels:
- Bad tunes kill them...
- Driving a Diesel like it is a petrol engine kills them (don't rev it to the red line - diesels aren't designed for that)
- Lots of short journeys where the engine never gets up to temp for long (big issue in Ireland now with every Tom, Dick and Harry buying Diesel due to the "Greens" meddling with the car tax system)
- VAG "Long Life Servicing"... definitely kills them stone dead.
- Stay away from the VAG v6 2.5TDI over 100k unless had a full rebuild... had several and all had issues -- mainly related to LLS and they're hard on juice too.
- 5 Cylinder 2.5TDI from VAG is way more economical and strong, very strong (had two of them, one with 400k kms on original engine and know person who bought who put another 120k on top and the other had 250k kms when I sold it and was perfect - no smoke, no oil use etc).
- 3.0TDI v6 is a good motor, hardy enough, very smooth, understressed, pretty economical... just need to forget about VAG service intervals and stick to 15k kms and still use the good oil.
- 2.0TDI is not as hardy as the 1.9PD and stay away from the 2.0TDI 170bhp version as they have huge oil consumption issues even from brand new.
Diesels are way more economical for high mileage when you add all costs together but you need to service them.
Most cars, petrol or diesel, in Ireland aren't worth "£$^&"@ after 100k miles due to bad roads and poor servicing