i had the same problem!
changed gearbox oil for redline MTL.........still crunched into 2nd
changed gear linkage bushes.............still crunched!
Final option changed gearbox for one i bought on ebay for £32!!!!!
did the clutch to whilst i was there as it was slipping at high revs!
this has put the novelty back into driving my gti!

if you dont get a result out of the oil or bushes definatly get another gearbox, its a piece of piss!!! im no mechanic but if your willing to learn and youve got plenty of time on ya hands its no problem!
