What was found
SHORTLY AFTER TAKEOFF, FLIGHT CREW NOTICED FLUCTUATION IN LEFT TORQUE METER, LOW OIL PRESSURE LIGHT CAME ON AND OIL SEEPING FROM THE LEFT COWLING. ENGINE WAS SHUT DOWN AND AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE INSPECTED AFT SECTION COVERED WITH OIL, BUT NO INTERNAL DAMAGE. SERVICED WITH OIL. GROUND RAN AND CHECKED FOR LEAKS, NONE FOUND. TEST FLEW, RECHECKED FOR LEAKS, STILL NONE FOUND. CREW STATED THAT OIL CAP WAS SECURE PRIOR TO TAKEOFF. SUSPECT CAP WAS NOT SECURE.