first box in mine, about 25k. the second, about 2k the third a whopping 30-odd-k nearly 40k.
it seems its not the box itself that breaks, rather the diff lets go and drops into the box mangling the insides (or blowing a bloody great hole in the side!)
i didnt drive it hard at all, and im not like a mate who is always having the same fauts with cars as he drives badly. This was the only car with a gear box problem i had. did 75k in a seat ibiza and all i had to do was replace rubbers in the linkage