You could pull the current tranny out and take it to a metal shop and see if they can repair the cast aluminum housing. I don't know too much about welding aluminum so it's prolly best that you call and ask if they could weld cast aluminum to begin with. Then see if they can fix it. If not try and find another GSR tranny and canibalize the part you need. I understand how you want to keep the tranny because it's a good one. So I would try the welding first and then go to buy a new one if it can't be repaired