1991 Subaru Legacy Problems

I need help. My girlfriends legacy just died and I have traced the problem to the gear attached to the main pulley. The problem is that the notch (where it attaches to the pulley) on the gear broke off and now the pulley doesn't stay on tight and I would assume doesn't turn the gear inside. Can this notch be welded on? Can I just have the pulley permanently welded to the gear? Does anyone have any suggestions on how this needs to be repaired???