I own a 1990 passat, I bought it with 108k miles. It now has over 180k miles. It has been one of the best cars I've ever owned. I had the heater core go out on me also, but VW replaced it for free under recall. You may want to give them a call and see if they'll still replace yours under recall. Just be carefull who you let work on the car. I do all the work on my car now, but when I first got it I took it too a mechanic to do the timing belt and some other stuff...well, to make a long story short I got the car back with about 3 more problems plus one of the problems that I took it in for in the first place and a 600 dollar bill. I ended up just fixing the car myself and have had very few problems with the car since. We have a good dealer in the area and they're the only ones that have ever worked on my car without creating more problems. Parts are very expensive for these cars, but I've never owned an american car that has gone over 180k miles on the original engine and transmission. There are places online like germanautoparts.com that has parts for very good prices, you just have to shop around...but if you buy parts from the dealer it will be way expensive...if you don't want the car you can always give it to me!!
Anyways, good luck.
Nick