What was found
DFW - FLT 1684 - DURING TAKEOFF, FLIGHT CREW NOTICED SMOKE IN THE CABIN. FLIGHT AIR INTERRUPTED AND RETURNED TO DFW WITHOUT FURTHER INCIDENT. UPON LANDING, SMOKE DISSIPATED FROM THE CABIN. MAINTENANCE FOUND THE APU OIL TANK FILLER CAP LEAKING OIL. REPLACED APU OIL TANK FILLER CAP, COALESCER BAGS AND RAN WITH PACKS ON WITH NO LEAKS OR SMELL NOTED. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)