I had the same problem. I repaired it by grinding the stud flat, then drilling and tapping the hole to the same size as the original stud. The thickness of the head on the old stud will give you 3 or 4 turns of the stud. Then I installed the new stud with thread locker and it has been holding fine. If you wanted extra strength you could braze the stud in after it was installed.
Garry
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