if its a synchro it will still go in 3rd it will just grind. if it won't go into 3rd at all he's probably been banging the gears too hard and missed 3rd real bad and bent the shift fork. and as boost4me said, does it go in now? or just last night it wouldn't? he could have just been having trouble because he was trying to shift too fast.
Well the tranny has to come out completely. You might just want to get a rebuild kit from promotionpowertrain.com or another tranny company. This will beef it up a little for the next time he tries to kill the fork.
Just my suggestion, you could always have a new stock fork put back in it but you know as well as us that he's going to run it hard throughout the future too.
My car will lock me out of 3rd as well sometimes. Very rare it happens but still happens.
he's better off getting a new trans or used one or rebuilt one. Seriously, once you account for labor, you just bought yourself a new trans almost. new trans are 1000ish and 1500 for a semi built one i think. I think i've been quoted around 800 to replace my syncros and thats just for labor. Shift forks should be the same labor cost.
But the 3650 trans just sucks in general so id take this opportunity and just buy a new trans that is semi Built(beefed up shift forks and syncros)