I went through that years ago, doing my slant seat tracks. I took some bolts and screwed them into something big and heavy to hold them in place, then took the angle grinder to the heads to form the odd little T shapes to them, cut the bolts to proper length welded them in place under the tracks and "voila"! nice new working tracks with new studs. The old, broken studs come out pretty easy, grind a bit of the old head underneath and use a punch and hammer and remember to brace the track up and pound old stud out.