I'm a fan of JB Weld but have also used Blue Magic Extreme. Both have very high temperature products. I used the Blue Magic QuikSteel Extreme on pin holes in an exhaust header a couple of years ago and the repair is still fine.
We used Belzona in the power plants I've worked on. It makes sound permanent repairs.
https://www.oreillyauto.com/detail/b.../37901/4388157
https://www.quiksteel.com/brands/QuikSteel.html
Get the surface very clean. I would use acetone for the final cleaning.