They're addictiveIs there anything I need to know about buying a TDI 90 ?
As with buying any used car there's risk involved. Your own experience proves that even the normally bulletproof 1.4 petrol can have its issues. If properly maintained I wouldn't say that a TDi 90 will be unreliable, but sometimes it's better the devil you know...
Like @Merlin3046, @Away with the fairys and a few others on here I have a TDi 90 with MYP 6-speed box fitted. The DMF and clutch were fine at time of gearbox swap (~90k miles) but it seemed sensible to get them done at the same time. It ticked over 100k miles last month and, touch wood, no turbo or other major mechanical issues for me so far.
I have a 40 mile round trip commute on a mix of A and B roads and it keeps the journey fun. I even have the rear seats out most of the time to save a bit of weight.