5th gear slips out! Help!

I have a b18c swap with gsr hydro to cable conversion. Before my selector shaft kept getting stuck in 3rd gear so I pulled it out and replaced the whole tranny with another one. Now after awhile with the new used tranny it did the same thing so I pulled it out readjusted the selector shaft and it’s fine. 4 weeks later 5th gear slips out… Put it in 5th and it’ll be fine at 35mph and if I give it gas it slips! This is my 3rd time pulling it out. Is the gears bad? It looks fine when I popped of the tranny cover. My selector shaft pin has a bit of a play.apparently. I wanted to find a b16 tranny but couldn’t. Tired of pulling the tranny off over and over. Also sounds like it’s winding in 5th with a lil bit of clunking . Is the bearings shot?. Any advise will help. And can I get new gears and just swap them out? Don’t want to get another bad tranny… New throwout bearing also. Clutch is fine. Resurface flywheel… Never touched it when I pulled the tranny out since it was pretty new

sounds like the gear itself could be bad, hard to tell about the clunking sound. whats wierd is its fifth gear, most of the time its 2nd and 3rd gear’s that go bad. you can replace just a single gear, but while your in there but you really should be replacing anything thats bad, I.E syncros, bearings, ect,ect…

as for the whining sound, is there a LSD in the trans.?