Funny, I ran into this post. FYI My car has GTX 3rd and 5th gears, a long with a fully rebuilt tranny. 95% new OEM parts used in the rebuild. Only used parts in there are the case and input shaft. When I broke the tranny for the 2nd time, I called SlowMotionMSP (previous owner), and he had extra parts that i bought from him (GTX gears).
PAR gears kept breaking because they are not meant for daily driving UNLESS you use the NEO synthetic gear oil, and change it every time you change motor oil. Straight from Gerard @ PAR. The wear that my gears showed was gradual pitting of the teeth, because of the oil being sheared more easily (straight cut gears and longer oil change intervals than required) which led to weak spots on a tooth, then that tooth would break off. Both times I broke teeth, I was babying the car.