VEHICLE PARKED; WHEN SLIDING DOOR WAS BEING OPENED IT CAME COMPLETELY OFF TRACK. WAS HELD ON BY TOP HINGE. IN PROCESS, DRIVER'S SHOULDER WAS INJURED TRYING TO KEEP DOOR FROM HITTING GROUND. THIS WAS THE 2ND INCIDENT THAT HAS HAPPENED WITH DOOR. AT THE DEALERSHIP, TECHNICAN REPLACED DOOR PART FIRST TIME. *AK