Any better ideas how to fix
Hi Thomas.
That is a real bugger discovering flaws like that; but it could be worse, right?
How heavy (thick) is the base?
If you were competent with tools, I was going to suggest a blind rivet, file then season.
That could be risky because of the stresses and the pan may not handle that :-/
You could clean the hole with a drill to suit the c/s screw you will be using, ever slightly countersink the pan from the inside, reduce a countersink screw to suit (with a clean shank and now no drive slot), then heat the pan well in the oven and follow on by brazing or silver-flo in the fastening. Dress up with a Dremel or such when completed. After a few seasons you may never notice it. Just like that paint(?) job we might do with that flaw that really bugs us; after a few weeks of use we cannot remember what all the fuss was about ;)
PS you could thread it and insert a m/c screw, braze in then cut the excess and finish with a rotory pad, Dremel or such?