What was found
WHILE TAKING THE RUNWAY FOR DEPARTURE, THE LT OIL LEVEL LOW STATUS MESSAGE POSTED. AT THE TIME L ENG OIL WAS AT 47%. OVER 15 MINUTES THE OIL QUANTITY ON THE LEFT ENGINE DROPPED TO 15%. THE LEFT OIL PRESSURE THEN DROPPED TO 5PSI OVER 5 MINUTES. RAN THE QRH AND RETURNED TO DEPARTURE. SERVICED THE ENGINE OIL IAW AMM 12-13-79 TO 100%. REMOVED THE AIR TURBINE STARTER IAW AMM 80-11-01. FOUND A CUT ON THE O-RING IAW 80-11-01. REPLACED THE O-RING IAW AMM 80-11-01.