A Heli-Coil will do the trick. (6x1.0) And it takes away less metal than the other insert. You'll have to cut off a couple of coils as there isn't a lot of depth to the threads. Stuff a greasy rag in there to capture the shavings. Although you can do the installation with the tranny in the bike, you might want to look at as a chance to do the input shaft spline lube.