I have actually seen that exact same issue on other boombox cassette drive gears as well, not just Sharps. I know that normal superglue does not work well on Nylon but there are some formulations of PLASTIC SUPERGLUE that does seem to work on Nylon, especially the ones that come with an applicator. I have also been been able to fix these types of issues by supergluing the gear to the shaft itself although admittedly, the ones I have done were better exposed and not buried in the middle.
As for printing the gear -- not so sure that would work successfully since it seems the printing process is not as precise as you would think. If printing a new gear, I would suggest that the hole be printed smaller than normal and the hold drilled out to the proper size. These gears are really precision and are press fit onto the shaft so the tolerances are pretty exacting. I think that if a good gear can be found, a mold can be made and replicas cast out of new material (not nlyon) that might could be glued onto the shaft for better grip. Some of the folks here have successfully cast new parts including some knobs with very fine surface striations -- quite remarkable actually.
