I HAVE SEEN THIS CRACK ON S&W 3 GEN BEFORE, 9MM AND 40's( YES AND SIGS, BERETTAS AND GLOCKS) . EACH TIME THE CULPRIT WAS THE RECOIL SPRING NEVER BEING REPLACED. THE RECOIL SPRING NEEDS TO BE REPLACED PERIODICALLY. THE HIGHER PRESSURE THE CARTRIDGE THE MORE FREQUENT THE REPLACEMENT. JP

P.S. I'M NOT SAYING THE NEW OWNER DIDN'T CHANGE THE SPRING IN A TIMELY MANNER. BUT BEING USED THERE IS NO WAY TO TELL HOW IT WAS DONE BEFORE HE BOUGHT IT. THE DAMAGE COULD HAVE BEEN DONE EARLY ON.