stripped seat belt bolt

I've had very little luck with extractors or welding over the years.
One good thing about having that type of bolt head is still having a center or pilot hole. If you start by drilling a 3/16 hole all the way through the bolt, then follow that with a 3/8 drill. There will be only a hull of the bolt left. If that wont turn with extractor, and it probably wont , drive a keen little punch in behind it . I grind a special purpose point on a drift just for this chore.
The hull should split and curl into the hole. Grab that with the needle nose and remove it or just drive it into the rocker. You'll have only to run a tap though the hole to correct the threads.

This is a sure fire method even though pains taking. A broke extractor in the bolt is a bad day.