VAG 2.0Tdi from 2005 had badly designed oil drive shaft, then without telling public VAG changed from chain driven to hex shaft drive, which in turn was better design overall but after high mileage would wear out just because it was a bit too short.
You could upgrade to longer hex shaft drive but that would cost you a premium (£300+).
If you wanted to upgrade from chain into hex drive then that would be even more monies.
Bur if you ignore all that, once drive shaft fails you better be looking for new engine.
Injector recalls/replacement on 2.0tdi are free, you just need to call dealer to confirm.
Latest 2008 onwards common rail tdi have sorted all shait out so are generally regarded as the ones to go for.
So if you go for early 2005 A4 its time proven older 1.9Tdi to go for.
IMHO