What was found
AT CRUISE ALTITUDE LT ENG OIL PRESS WENT TO 85 PSI & CONTINUED TO DROP. OIL WAS OBSERVED COMING FROM THE LT ENG BEHIND THE PROPELLER, AT 65 PSI ENG WAS SHUT DOWN. AN EMER WAS DECLARED & ACFT DIVERTED. SECURED THE OIL VENT LINE FROM THE TORQUE TRANSMITTER AT THE POWER SECTION CASE. ENG WAS SERVICED WITH OIL. ENG GND RUNS PERFORMED WITH NO DEFECTS NOTED. A SUCCESSFUL OPERATIONAL CHECK FLIGHT WAS PERFORMED & A POST OCF INSPECTION WAS ALSO PERFORMED WITH NO DEFECTS NOTED. ACFT WAS RETURNED TO SERVICE.