What was found
(CAN) AFTER ARRIVAL AND ENGINE SHUTDOWN WITH APU AND AIR CONDITIONING SYSTEM OPERATING THE CABIN FILLED WITH SMOKE. PASSENGERS WERE DEPLANED NORMALLY IN A EXPEDITED FASHION. AIRPORT FIRE DEPARTMENT CAME AND INSPECTED THE AIRCRAFT. FIRE DEPARTMENT TOOK NO ACTION. MAINTENANCE INSPECTION FOUND SIGNIFICANT OIL CONTAMINATION OF THE APU COMPRESSOR AND SUSPECT A FAILED INTERNAL OIL SEAL THAT LEAKED OIL INTO THE COMPRESSOR WHICH CAUSED THE SMOKE INTO THE CABIN. APU REPLACED AND FUNCTION CHECKED WITH NO FURTHER ISSUES. (TC# 20190613004)