I drive a 90TT with 175,000 miles and it still runs great. I change the oil about 3k or so I use mobil 1. I think if you drive the car and not abuse it it will last.
One thing you must understand is that after a while you will have little problems with any car. Your best bet is to buy a manual and learn how to do your own repairs this will save you tons of money. Preventive maintenance is the key. If you stay on top of things before they happen then you'll save yourself a lot money. I hear people say the 90TT was not a good car. I don't believe that at all I bet there are a lot TT that didn't make 175,000. I hope this did help a little.