What was found
THE ACFT HAD LANDED AND WAS BEING PUT AWAY WHEN THE PILOTS NOTED THERE WAS OIL LEAKING FROM UNDER THE LT SIDE OF THE COWLING; THE LEAK TRAVELED THE LENGTH OF THE FUSELAGE AND HAD COATED THE LT WING AS WELL. THE PILOTS ALSO NOTED NO OIL WAS VISIBLE ON THE DIPSTICK; THEY HAD DEPARTED WITH 8 QUARTS AND FLOWN 1.4 HOURS. MAINTENANCE FOUND THE OIL COOLER WAS LEAKING FROM INSIDE THE PLEATS AND THE ENGINE HAD 3.5 QTS OF OIL LEFT, A LOSS OF 5 QTS IN 1.4 HOURS. THE OIL COOLER WAS INSTALLED NEW, THREE WEEKS PRIOR.