Making collars for gear repairs is easy.

Hobby shops usually carry brass, aluminum and plastic tubing in various sizes. You may even have in your collection of "I'll keep that. I might need it someday"  items, old chrome plated, telescopic radio antennas. (I do - of various sizes)

I use an electronic caliper to measure the ledge on the plastic gear and the inside of the tubing to be sure of a snug fit.

1) Before cutting  a collar from a tube, flare the end of the tubing  (just a little bit) every time, for each collar. The reason will become obvious when you attempt to press-fit the collar to the ledge on the gear.

It's not worth cutting the tubing with a hack-saw or with a moto-tool.  Otherwise you will have to spend a lot of time de-burring the end(s) of the tubing. 

2) With a small pipe cutter and slow, steady, pressure adjustments on the cutting wheel, you can cut collars that will work, on nylon gears, provided they do not hinder performance. ( I know.  I did it hundreds of times in my job.)

Once you cut the collar from the tubing sand it lightly with a fine emery paper so there are no sharp edges on the collar.  Now, you will have a collar that should be able to be press-fitted onto the ledge of the plastic gear.  Remember, the inner edge of the collar has been flared for easy starting and the outer edge is partly rolled in (from the cutting process) to ensure a snug fit.

Press fitting can be done various ways.  However, remember you are working with a plastic gear and you do not want to cause any other damage to that gear.  If you are not sure how to press fit the collar to the gear, let me know.  I will tell you how I do it. (I need to get ready for work now)

Provided the gear only has one split, press-fitted collars make perfect sense.  If it is broken in two places, replace the gear.

Remember, be innovative. It's not against the law.

G.T.