I had a stock b13 trans in my car, took out the gearstack, bought a whole new gearset with the 5th gear popout kit from Courtesy, had the new gearset cryo treated and shotpeened. Within two months I had 5th gear popout, another month after that 5th gear was nearly useless unless I kept my hand on the stick. Within a month after that, 4th gear self destructed under half boost and half throttle (something like 7psi and 50% throttle). So, I'm with stratton. All that time and energy was wasted and the trans went anyway. I'm currently running a b14 trans because it was super cheap and available the day after the trans went, but as soon as it pops I'll go p11 for sure.
IMHO the b13 trans is definitely doomed and you should just make plans ahead of time to replace it with something better.