What was found
LANDING GEAR WOULD NOT RETRACT WHEN 'GEAR UP' SELECTED. SNOW, ICE AND SLUSH WERE SUSPECT. AIRCRAFT WAS JACKED AND CLEANED OF ALL MOISTURE AND GEAR OPERATED NORMALLY. AFTER TAKEOFF WITH DE-ICED GEAR, LANDING GEAR DID NOT RETRACT AGAIN. AIRCRAFT WAS JACKED AND TROUBLESHOT. AFTER SEVERAL CYCLES, GEAR FAILED TO RETRACT. THE MAIN GEAR DOOR SELECTOR VALVE WAS DETERMINED TO BE INTERMITTENT AND WAS REPLACED. GEAR WAS CYCLED NORMALLY ON JACKS AND TEST FLOWN NORMALLY.