What was found
AFTER BOTH ENGINES WERE STARTED AND WITH AIRCRAFT CONFIGURED NORMALLY, THE LEFT DUCT PRESSURE WOULD OSCILLATE BETWEEN 10 AND 40 PSI WHILE RIGHT DUCT PRESSURE WAS STEADY AT 35 PSI. THE OSCILLATION TOOK APPROX 20 SECONDS FROM 10 TO 40 PSI THEN REMAINED AT 40 FOR 20 SECONDS, THEN DROPPED BACK TO 10 PSI FOR 20 SECONDS AND REPEATED, FROM AFTER PACKS WERE TURNED ON TO TOP OF CLIMB. IN CRUISE, THE LEFT DUCT PRESS REMAINED EVEN WITH THE RIGHT DUCT PRESSURE AT 35 PSI. FOUND SEALS ON #1 ENGINE HPSOV WORN AND CAUSING LEAKS. REMOVED AND REPLACED SEALS IAW 767 AMM 36-11-07. RAN #1 ENGINE, NO FLUX NOTED. BITE BOX NO FAULTS AT THIS TIME.