You may want to look into Velocity limited slip diffs or give Kraftswerk
(714) 901 5055 a call.  The Velocity unit is not as complex as the Quaife
but costs about $100 for the Golf/Jetta application.  The Quaifs have about
40% lockup while the Velocity only has 15-20% but costs a tenth of the
Quaife.  My brother has a Velocity unit is his GTI 2.0L 16V that works very
well.  His transmission was built by Kraftswerk who can do custom gear
ratios and sell the Velocity limited slip diff.

dave