What was found
DURING CRUISE FLIGHT, OIL PRESSURE ON NR 1 ENGINE DROPPED TO 22-24 PSI AND ILLUMINATED NR1 ENG OIL PRESS CAUTION LIGHT. REDUCED NR 1 ENGINE THROTTLE TO IDLE AND INDICATED OIL PRESSURE STABILIZED IN THE LOW GREEN TO HIGH YELLOW, 22-24 PSI. RETURNED TO DEPARTURE WITH NR 1 ENGINE THROTTLE AT IDLE, ON FINAL FOR A RUN-ON LANDING WE RETURNED NR 1 THROTTLE TO FLY BUT NR 1 ENGINE OIL PRESSURE DROPPED TO RED 17 PSI SO RETURNED THE NR 1 ENGINE THROTTLE TO IDLE AND ACCOMPLISHED THE RUN-ON LANDING. WHILE TAXIING IN SHUTDOWN THE NR 1 ENGINE. NO SECONDARY INDICATIONS WERE OBSERVED IN FLIGHT. FOUND AXIS-B ENCASED FLANGED SEAL IMPROPERLY INSTALLED.