When you install the trigger guard roll pin, you must back up the bottom ear.
Basic run down is to chuck up the roll pin in a drill, taper the edge of the roll pin that you will diving first, install the guard, then using a Puck type block and back up the bottom side ear so the pin force is only to the pin hole area on the block, and not acrossed the surface all the way to the receiver edge of the ear (read bottom ear not backed up).
Now having said that, this still doesn't help you on this build since you have already snapped the ear off. If the game plan is never to drop the guard for a winter trigger, then Epoxy, and the tension of the roll pin should hold the snapped ear in place. As for going to the trouble of milling and welding, there is the matter of removing the anodizing to weld, the having the receiver/new parts re-anodized. About that point, it's just cheaper to buy a new receiver.
Welcome to the site!!!!!!
(But I just hate to be the one to drop this bomb on you during your first post).