What was found
TAXIED OUT FROM FBO, WITH APU RUNNING, WITH BLEED AIR ON. GOT TO THE END OF RUNWAY, NEXT FOR TAKEOFF WHEN A LIGHT BLUE COLORED SMOKE STARTED TO FILL THE COCKPIT AND CABIN. TURNED BOTH BLEEDS OFF RETURNED TO GATE, SMOKE DISSAPATED. REPLACED WATER SEPARATOR COALESCER SOCK. TROUBLESHOT TO A CUT O-RING ON THE OIL FILLER CAP AND APU OIL TO BE OVERSERVICED. REPLACED OIL FILLER CAP O-RING WITH A NEW O-RING SERVICED APU OIL TO LIMITS RAN APU TO PERFORM OPS AND LEAK CHECKS OPS AND LEAK CHECKS ARE GOOD. WORK DONE IAW MM 48-00-00 AND MM 49-22-00.