Stepper motor shaft rotating inside worm gear

I have a Version 2 SatNOGS rotator, which works well for the most part, but I noticed that the Elevation gets wrong after a few hours of operation. Homing it (by power cycling) corrects this, but I have noticed that sometimes the EL stepper is running and I have to manually help the antenna to come back to home. The problem seems to be that the stepper motor shaft is rotating inside the worm gear. The gear opening is D-shaped (matching motor shaft) and I have the threaded pin in place (which is supposed to prevent this); but apparently the torque requirement is more than the ABS plastic can handle. Has anyone else hit this problem and solved it? (I have polished the gears and applied good silcone grease)

I can imagine using a very good drill press (which I don’t have) and drilling a hole through the stepper motor shaft (which will be a pain because there is a LOT of disassembly to get the motor out), and a pin through the shaft (instead of on the side of it); but I am looking for better suggestions. Anyone??

If the hole isn’t too eccentric and there is only a small gap then anearobic adhesives might be worth a go. They don’t like a big gap and need the absence of air to cure but stuff like Loctite 601 is very strong once it has cured. They tend to work best with metals and will crack certain plastics so try it on something else first. Otherwise its disassembly and epoxy.