4 spd. pops out of gear.

I bought a 833 from a member here decade+ ago, was told good. The build took me a decade to finish and put into service, he lied... Any how The gears grind in all forward speeds unless slow shifting and pops out of 2nd only on deceleration.

I been wanting to rebuild or replace this trans. I inquired @ Brewers if their rebuild kit would solve these issues before I wasted $ on a kit and tearing it down.
Their guy said I would probably need to send in the 2nd gear for machining.
I asked what is done, build up of gear and machined back to size? He said no I just file the synchronizer . I don`t consider machine work and file work the same.

Any of you guys rebuild a trans with issues like this and have solved with the basic rebuild kit?
Thanks.