I had a 300tdi

They are slow, sloppy,noisy and you get around 24mpg.
The electrics are fucking awful, dash lights fail, stereo controls fail.
Sunroofs leak and get under the carpet in the footwells and then rot the floor. heater matrixs leak begind the dash and cause electric issues.
Rear boot floors are notorious for rusting, you must check under the carpet before you buy. Sills rust as bad as the boot, inner wings rust at the bottom where they all collect water. Door handle springs snap inside and then you cant open the doors, very common.
Cruise control is always an issue as the hoses perish.

The best buys are the basic models, ie, no heated seats, no electric seats and no sunroofs.

Best and cheapest mods are, decat downpipe @20, and bypass the EGR £20. You get more power and better mpg

Apart from that...its all good

Regards

Leigh