What was found
SMOKE IN THE COCKPIT. APU WAS STARTED ABOUT FIVE MINUTES PRIOR TO LANDING & WAS OPERATING NORMALLY. UPON LANDING & TAXI IN APU QUIT DURING ENG SHUTDOWN. WE THOUGHT WE HAD BUMPED A SWITCH. AFTER THE PAXS DEPARTED ABOUT FIVE MINUTES WE TESTED, GOOD TEST & RESTARTED THE APU & SMOKE & FUMES IMMEDIATELY FILLED THE COCKPIT. SMOKE SEEMED BLUE COLORED & THE FUMES SMELLED LIKE FUEL. WE DID THE ACFT EVACUATION PROCEDURE, EXCLUDING ENG FIRE SWITCHES & BOTTLES BECAUSE ENGS WERE OFF. ALL SYS WERE SHUTOFF. THERE IS A STRIP OF OIL LIKE SUBSTANCE INSIDE THE HELLHOLE DOOR WHICH WAS NOT PRESENT PRIOR TO FLIGHT. R & R APU. SYS OPS CHECKED GOOD IAW MM 49-10-00.