TL*THE CONTACT OWNS A 2006 GMC SIERRA 1500. THE CONTACT STATED THAT THE MASTER CYLINDER FAILED ON HIS VEHICLE. WHILE DRIVING AT AN UNKNOWN SPEED, THE BRAKE PEDAL EXTENDED TO THE FLOOR AND THE VEHICLE FAILED TO STOP. THE CONTACT REAR ENDED ANOTHER VEHICLE. THERE WERE NO INJURIES. THE FRONT END, HOOD, AND GRILL WERE DAMAGED. THE VEHICLE WAS TOWED FROM THE SCENE AND RETURNED TO THE SHOP IT WAS REPAIRED AT THREE MONTHS PRIOR TO THE CRASH. THE TECHNICIAN STATED THAT THE MASTER CYLINDER WAS THE CAUSE OF THE FAILURE. THE CONTACT HAS CALLED DIFFERENT GMC DEALERS AND REPAIR SHOPS TO PURCHASE A MASTER CYLINDER, BUT THERE ARE NONE IN STOCK. IT WOULD TAKE A WEEK FOR THE PART TO ARRIVE SO THAT THE REPAIR CAN BE COMPLETED. THE FAILURE MILEAGE WAS 50,000.