I PARKED ON A DRIVEWAY WITH A 15 DEGREE PITCH. I FOLLOWED THE SAME PROCEDURE EACH TIME I PARK, WAITING 1 MINUTE IN IDLE, TRANSMISSION TO NEUTRAL, WITH MY FOOT DEPRESSED ON THE BRAKE PEDAL. AFTER SHUTDOWN I ENGAGED THE PARKING BRAKE AND PLACED THE TRANSMISSION IN 1ST GEAR. I EXITED THE VEHICLE FOR 10 TO 15 MINUTES PREPARING THE CAR FOR WAXING. I LEFT THE AREA FOR ABOUT 15 MINUTES AND RETURNED TO FIND THE CAR HAD ROLLED DOWN THE DRIVEWAY, CRASHED THROUGH A FENCE, DOWN A HILL, AND INTO TREES. (THE PARKING BRAKE WAS ENGAGED BUT TRANSMISSION WAS IN NEUTRAL) I PERFORMED TESTS AND DETERMINED THAT RANDOMLY, GEAR SHIFTER APPEARED TO BE IN 1ST GEAR BUT WHEN I RELEASED THE PARKING BRAKE THE SHIFTER RETURNED TO THE NEUTRAL POSITION AND CAR STARTED ROLLING BACK. I CONTACTED VW CUSTOMER SERVICE AND REPORTED THIS. A VW SERVICE MANAGER ASKED ME TO REPLICATE CONDITIONS OF INCIDENT. I PARKED THE VEHICLE ON A SLIGHT UPGRADE, ALLOWED ONE MINUTE IN IDLE, SET THE PARKING BRAKE, AND PLACED THE SHIFTER IN 1ST GEAR. THE SERVICE MANAGER INFORMED ME THAT MANUAL TRANSMISSION SYNCHRONIZERS CAN RANDOMLY CATCH WHILE STATIONARY PREVENTING PROPER ENGAGEMENT INTO 1ST GEAR. HE ALSO INFORMED ME THAT I HAD NOT FULLY ENGAGED THE PARKING BRAKE. HE PULLED THE PARKING BRAKE UP SLOWLY (APPROXIMATELY 6-7 CLICKS). THE SERVICE DEPARTMENT REPORTED PARKING BRAKE AND TRANSMISSION TESTED OK AND NO REPAIRS REQUIRED. QUESTIONS FOR NTSB: 1 SHOULD ORDER OF OPERATIONS OUTLINED IN VW OWNER'S MANUAL FOR PARKING CAR WITH MANUAL T