Repairing a crack in a hard nylon part

The JB Weld on the head mount is still holding. For the last couple of years, the player has become my workhorse player and gets used at least a few days each week.

I bring this up again because I just had the player apart today to swap out the over-polished capstan. I have a parted out 8-track unit that happens to use the same capstan so I swapped it out of that. The capstans really require a sandblasting to give them the proper grip, I don't have a sandblaster so I have to either use 240 grit sandpaper done in a cross-hatch pattern or PCB etchant (ferric chloride). The PCB etchant gives it more of an original feel but it isn't deep enough so it wears smooth after several hours of playing. The sandpaper lasts a little longer but also wears smooth too quick. They originally sandblasted the capstans with something similar to that used to clean spark plugs which lasted many many hours before getting too smooth.