S40 Racecar help

[gothev8]

Hi All, I am new to the site and I am hoping I may be able to get some help about my S40. I have built a 1998 S40 T4 into a race car which I use to race in endurance events (track). The engine is fresh with strengthened internals including H beam rods and Wiseco pistons (standard size and compression) and heavy duty valve springs. I am running the stock turbo and the engine is producing 200hp at the wheels at 15 pound of boost. The front suspension has been swapped for Evo 8 with Brembo brakes and the rear is Mitsubishi FTO 5 stud with Evo Brembo brakes to match the front. The rest of the car is basically standard apart from XYZ Coilovers and a Quaife ATB LSD. I wanted to build a Volvo for something different but they aren't popular in Australia and it's hard to get good advice. For the most part the Volvo is quick and reliable except for 1 thing, the gearbox. I am constantly braking the 3rd- 4th gear selector fork and I have no idea why. I get 50 laps into a race and it starts to go and by 100 laps I am out of the race. This has happened twice now, the second time it was a brand new fork. I have found a performance shop here that can make me a billet fork but I suspect there may be more to this issue.
My question is, does anyone know why this is happening and is there a solution?
Many thanks,
Greg

[alschnertz]

All North American S40s were automatics.

Try your query on volvospeed too. Not saying no one here would be willing to help, it's just that a manual gearbox in a S40 would be very unusual here.