Regardless, however the gear was mounted and driven, there was once more material around that slot that is all worn. I would suggest that someone worked it hard, drove it to the stops all the time, or cranked it without releasing the brake. This wore the slot and eventually broke. I'd take out whatever is in the hole and replace. Figure how to keep all the gears in proper alignment. If the gear is steel, you could have it filled by brazing and re-slotted. Or you could fill with epoxy. Just don't drive it to the stops.
best of luck
Bookmarks