Thats cast aluminum. A pretty difficult weld to begin with.
And it is highly likely that cracks radiated through the casting before that chunk broke off.
Aluminum castings do not like to bend.
If this was a big money racing transmission and I need a couple of more runs out of it.
I would pull the torque converter, stick a chunk of fire blanket inside the bellhousing, torque it back to the block then backgouge the hell out of the broken part and hope I could get at it with a spool gun after I preheated it and tried not to light myself on fire while I washed it down with acetone before each pass.
Aluminum instantly corrodes.
The minute air hits it
If It was a bone stock transmission that I just rebuilt, I would try to get a boneyard case and swap the parts.
It its a high miler?
It isnt worth what you will have to pay a good welder to try to fix it.
A good time to rip it down and learn how a transmission works.
