I had this gear from a DSG lathe to repair. It had one single busted tooth on it, probably from being dropped as there was no other damage at all. I decided to fit a new piece in and cut the one single tooth with an involute cutter. Here's the gear. 90 teeth 12DP 14.5PA. An inch thick with a 1.25" bore. I milled a slot in it where the broken tooth was. Then I cut a piece from a slab of grey iron I have kicking about for no purpose. Milled the piece I cut to fit in the slot nice and snug. There were four possible orientations so I picked the best and marked it with an arrow. Bonded it in with a high-strength structural araldite. Not your ordinary stuff this is £25 for a small tube. I put it in my mill to keep the load on it for a couple of days of curing. I thought about brazing in the new piece but I wasn't sure if the red heat would affect the grain structure of the adjacent teeth and make them weaker or more brittle. I figured that a good fit and some decent adhesive should hold that piece in very well. I suppose a scotch key could be added for peace of mind, if the owner was worried. Once the part was cured I stuck in in my chuck to turn the OD. I put a piece of thin card under one jaw with the block dead opposite and this gave it a few thou runout so that I could just turn it down until it skimmed the adjacent teeth half a thou. Did one half width then turned it around to do the other side. Gear now ready to have the new tooth cut.