[Tom Line]

If you are talking about the external plastic coupler, you can try this:

Get a nice 2 part epoxy. JB Weld will work in a pinch and can be bought in smaller amounts. If you were a sailor I'd recommend West or something else with a colloidal silica mixed in for strength.

Put a piece of saran wrap over the drive shaft that comes out of the motor. Mix the epoxy and put it into the plastic coupler. Put a pretty decent amount in. Press it onto the saran wrap. The saran wrap is acting as a release agent.

Once it's dry, slide it off, peel out the saran wrap, and use a dremel to remove the excess epoxy.