okay this is a long story so please stick with me.
i got this little d-50 5mt 4x4 from a neighbor and he got it from another neighbor, when the first owner had it, it got stuck in two gears, at least that was what i was told. when my other neighbor got it, he pulled the trans and was able to fix it, kind of. dont ask me how he did it, i don't know, but now when you shift into first when moving it feels like it goes in, acts like its in neutral. if you stop completely and put it in reverse, second then first it will shift in, but it feels week. i have been carefull not to force it into gear.
just a little while ago when i was in a parking lot i backed into a spot and shut it off then let it sit for a few minuets. when i got back out to it, and started it it was stuck in gear, but it felt like it was in neutral. i carefully messed with it a bit and was able to get it out of gear and get started in second (i didn't even want to mess with first) everything seems to be back to the way it was before, but i decided to pull the shifter and inspect it. it looks like someone ground something down on the shifter and it has alot of slop.

what im wondering is what could be the problem and should i try and fix it or just say screw it and get another trans and keep this one for parts.

another question would be where would a good place be to find a good trans for this and is this a fairly common problem that i should look for

thank you ahead of time for your time. i appologize for the bad grammer and i hope that it doesnt turn away any of the more knowledgeable people on here