If you don't want to cut out the bad metal & weld in a patch then what you can do is cut a piece of sheet metal bigger than the area, drill a hole for the seat rail stud to go through, use some JB Weld on it to help secure it, as well as rivet or screw down the patch. What you might want to consider is to sandwich the split metal with another piece of metal under the car before bolting up the seat.