Someone tried to peen a rail with a ball-peen hammer (I'd think). If you just need to be old school and peen a rail, use a flat faced body hammer. Snap on makes great hammers with a nice polished surface. Ball-peen hammers have too rounded of a face to do the job correctly.
Which meant welding up the area that was peened.
Doing it right means welding the area up. Micro-TIG works, but using a laser means no undercutting and a cleaner weld.
Sorry it took so long DB.