I recently purchesed a 2004 jetta with 107,000 with a tranny the didnt go in reverse. After leaving the dealer and taking the car home i found that it did reverse. The thing is, it doesnt always engage. It seems lik its in neutral. but if i sit with it in reverse for a couple minutes it well suddenly engage. Other times it well work perfectly. Any ideas what it could be?? i am prepared to rebuild it. but if it could b something cheaper it would b nice. Any ideas well help a lot thank!

2004 jetta 1.8T
auto 5 speed tiptronic
paid $3800 for it.