In the Steve Smith how to book (How to build a mini stock pinto)he shows that the best way is to fill (weld) the area between two (2) teeth with brazeing. Then rotate the gear and do the same thing 180 degs from the first place. Do both the gears this way. Brass is used because the book says that arc or mig place too much heat into the gears and will cause failure. I have done several cars this way with nary a failure to date. It can be done on old gears but much easyer on new gears.