There's some very very expensive rocket tech stuff that would probably work but the head would still have to come off and having it welded would probably be cheaper even if you could find a supplier for the other other stuff . Sorry again bud .............

 

if the thread is worn or stripped, use a Heli coil. you can get them at an auto supply. Drill and tap with the provided tap, red loctite and insert the coil you keep the original bolt size and have a new thread. also they make an exhaust gasket shellack mostly used on donuts