What was found
(CAN) DURING FLIGHT SMOKE BEGAN TO FILL THE CABIN. THE AIR CONDITIONING SYSTEM AND RH AC BUS WERE ISOLATED. FLIGHT CONTINUED TO DESTINATION. POST FLIGHT INSPECTION FOUND #3 PROPELLER VALVE HOUSING COVER WAS CRACKED AND LEAKING OIL. FRICTION ON SLIP RING GENERATED SMOKE WHICH WAS INJESTED BY THE PRESSURIZATION SYSTEM. VALVE HOUSING COVER, SLIP RING AND BRUSH BLOCK WERE REPLACED AND AIRCRAFT RETURNED TO SERVICE.