145 TS owner reporting in.
Well, not that many left unfortunately. Service history is very important, there you can see what and when was changed and what oil was used and how regularly was it changed. I was lucky and my 145 has a fully documented service history, impressive for a 23 year old car. It doesn't burn and it doesn't leak oil.
As others have noted, rust is a problem. Because the body was galvanized in the factory, the exterior of the car can fool you. It mostly roots away where you can't see it, like the radiator mount and the body work mounts that are bolted to the body of the car, underneath the drivers seat and inside the wheel arches. Inspection should be detailed and comprehensive.
On the TS version almost certainly the variator is bad. If the car sounds like a diesel engine when starting, it's the variator. Doesn't impact much of the performance or economy and it costs about €100+ to replace. It's replaced with the timing belt because it has to be off when replacing anyway. Most don't replace after the second time it goes bad in 100k km.
Plus other stuff you would watch out for on any car.
If you have any questions, I'd be happy to answer them.