What was found
AT 34,000 FT AND CRUISE MODE, OIL QUANTITY OF LEFT ENGINE WAS NOTICED TO BE AT ZERO WITH NO OTHER ABNORMAL ALERTS. OIL PRESSURE WAS AT 35-37 WHICH WAS ABOUT 20 PSI LESS THAN THE RIGHT ENGINE. THE PRESSURE SLOWLY CONTINUED TO DROP UNTIL RED LINE AT ABOUT 10 PSI. REFERRED TO CHECKLIST AND SHUT DOWN THE LEFT ENGINE. TEMPERATURE REMAIN NORMAL THROUGH OUT PROCEDURE. SINGLE ENGINE AUTO-LAND WAS ACCOMPLISHED AT GEG RUNWAY 21. EMERGENCY DECLARED AMM: 72-64-02-4 REPLACED STARTER ACCESSORY GEARBOX CARBON SEAL FACE AND MATING RING SEAL. AFTER INSTALLATION OF STARTER AND VALVE, OPS/LEAK CHECK REQUIRED. REINSTALLED SAME STARTER AND START VALVE. OPS CHECK NORMAL, NO LEAKS NOTED. WORK ACCOMPLISHED REF B767 MM 80-11-01-4.