What was found
(CAN) IN CRUISE PILOT OBSERVED OIL SPRAYING ONTO THE WINDSCREEN. AS HE WAS CLOSE TO A MAINTENANCE BASE HE ELECTED TO LAND AND HAVE IT LOOKED AT. AT LANDING HE NOTICED OIL PRESSURE HAD DROPPED TO YELLOW (70 PSI AND THE LOW OIL PRESSURE LIGHT HAD FLICKERED ONCE. AFTER NORMAL SHUTDOWN THE MECHANIC FOUND A DEFECTIVE O-RING AT THE TUBE UNION AT THE ENGINE C-FLANGE. O-RING WAS REPLACED , 4 LITERS OF OIL ADDED AND GROUND RUN NORMAL. CHIP DETECTOR AND OIL SCREEN WAS CHECKED CLEAN.