You could try having the lock up rates of the diff ramped up. As I said, standard items just aren't designed to take the abuse of track use. Fit an uprated item and it saves you money in the long run.

I was the same as you when I had me Sapphire 2wd - I thought that it would be cheaper to keep buying 2nd hand diffs at £250 a pop, 18 months and six 2nd hand diffs later, I wish I'd just fitted an ATB in the first place - cost me twice as much in the long run . I then bought the Quaife and had no more trouble with the car for the next 20k miles with 500bhp and LOADS of abuse .