I think TIG/MIG welding in a new bung would probably be my best option. Unfortunately, I don't weld. More unfortunately, I can't seem to find anybody local who will do it - even exhaust shops won't do the work. So for now, that leaves me with the liquid welding option.
I have tried JB Weld (rated up to 500*F) , Inferno weld (rated up to 2000*F), and some generic exhaust repair from Advance Auto (rated up to 1600*F). Believe it or not, the Advance Auto stuff held the longest.

