I know you said it should be VAG, but I still think the Land Cruiser Amazon V6 diesel is the best off-roader out there in terms of reliability and hardiness. Its got the amazing gear-driven engine, no chains or belts to snap.
If you can find the rare non-turbo version is even hardier, so little to go wrong.
They look really good too.
http://d1r57ja1amoclf.cloudfront.net...1997_HiRes.jpg
My mistake, is a I6 diesel not V6.
The non-turbo is the legendary 1HZ engine.
https://en.wikipedia.org/wiki/Toyota_HZ_engine
*edit*
on the other hand the 1HZ non-turbo Amazon does sound a bit underpowered, maybe not a great reccomendation.
http://4xoverland.com/turbo-charging...ta-1hz-engine/