What was found
AFTER TAKEOFF FLIGHT CREW NOTED SMOKE IN THE CABIN & COCKPIT. CREW DECLARED AN EMERGENCY AND RETURNED TO GCM. MAINTENANCE FOUND APU INLET CONTAMINATED WITH OIL DUE TO A LEAK AT THE SIGHT GLASS & THE FILL HOUSING TO GEARBOX SPLIT LINE. MAINTENANCE RETORQUED SIGHT GLASS AND FILLER MOUNT HARDWARE, NO FURTHER LEAK NOTED. MAINTENANCE CLEANED APU INLET DOOR ASSY & SURROUNDING AREA. PACK BURNOUT PERFORMED AND THE AIRCRAFT RETURNED TO SERVICE.