I just repaired a tooth on my broken bull gear. I used that water mix strong putty (the one with the strongman on the can). A couple of tips: use mold release agent (else it will stick and break), wait until long after it sets (else it is not strong enough), shave off one face so there are no bits getting in the way of a clean axial slide, and only slide it off axially (radial yanking will crack it). As you can tell, it took a few tries. When using it to measure, only slide it axially. Measure the widening gap at the new tooth as you are filing to fit. It is good for about 2 or 3 checks, then the tooth breaks off. Clean it up and use the next tooth. When you get close, fit it so that the new tooth is in the middle of the arc. If it has a clean slide, you can go to the real gear fit with bluing for high spots. Do not force anything.