What was found
AIRCRAFT PERFORMED AN UNSCHEDULED LANDING, THE LT ENGINE (OIL PRESS LOW) LIGHT TURNED ON. CAPTAIN INFORMED THAT DURING CRUISE THE (OIL PRESS LOW) LIGHT TURNED ON, PERFORMED THE EMERGENCY PROCEDURE AND LT ENGINE WAS SHUTDOWN. DURING MAINTENANCE REVIEW, THE OIL INDICATION WAS ZERO QUARTERS, THE ENGINE COWLINGS WERE WITH OIL EXCESS AND AN OIL LEAK WAS DETECTED IN DIFFERENTIAL PRESSURE SWITCH. 16 QUARTERS OF OIL WAS CHARGED AND ENGINE WAS RUN. AT 25 PSI OF PRESSURE, THE LEAK WAS EVIDENT ON A HYDRAULIC TUBE OF THE DIFFERENTIAL PRESSURE SWITCH CONNECTION. HYDRAULIC TUBE WAS REPLACED IAW MM 79-30-00, ENGINE WAS RUN AND GCU WAS RESEATED, TESTED CORRECT.