What was found
(CAN) PILOT REPORT THAT HE HAD JUST LEVELED OFF WHEN, THE COCKPIT FILLED WITH SMOKE. THERE WAS NO INDICATOR THAT ANYTHING WAS WRONG. PILOT RETURNED TO AIRPORT. UPON ARRIVAL IT WAS NOTICED THAT THERE WAS EXCESSIVE OIL LEAKING FROM THE ENGINE. THE COWLING WAS REMOVED AND FOUND. THAT THE REDUCTION GEAR BOX CHIP DETECTOR HAD SEPARATED BETWEEN THE FLEX. AREA OF THE CHIP DETECTOR AND THE BASE OF THE THREADS. OIL LEVEL WAS CHECKED WITH A LOSS OF APPROX 4 LITERS.