Low Gear Won’t Engage

I recently got a 1997 Polaris 6×6 that I’m going over, cleaning up and starting to use… Hi and Reverse work OK (new to these machines so I don’t know how it SHOULD do) but anyhow when I try to use LOW: shift lever moves, the linkage and shift ear on outside of trans both move but the gears inside don’t engage… Before you say the engagement collar is busted inside– I took the transmission apart and on the bench it shifts in and out of gear OK– but when I put it back into the ATV… Same thing: HI and Reverse work OK, but it takes a BUNCH of fiddling with it to get it to engage into LOW.
Guy I got it from said that in all the time he had it He doesn’t recall having ever even shifted into LOW for anything. But for what I plan on using it for I think that LOW might be a must-have. Any Thoughts???