i wouldn't repair it.... break the car and then buy one that works!! I had this with my first gti.... the gearbox let go and i paid silly money to get that sorted, then the suspension broke and i got that done and then it failed the m.o.t on emmisions and I gave in and decided to buy another...lucky really as when i broke it loads of dodgy/bodged up bits became aparant!!
or if your adamant and really want to keep it try robiwill on here (check the parts area) and see how much he wants for a full top end or engine...