What was found
(CAN) ON ROTATION OUT, CREW NOTED NR 1 OIL PRESSURE WARNING LIGHT ILLUMINATED, AND LARGE STREAK OF OIL ALONG INBOARD SIDE OF LT NACELLE. CREW ELECTED TO SHUT DOWN NR 1 ENGINE (HAD TO USE ALTERNATE FEATHER PROCEDURE TO FEATHER THE PROPELLER), AND RETURMED TO BASE. AIRCRAFT LANDED WITH NO FURTHER INCIDENT. MAINTENANCE REVEALED NR 1 OIL COOLER LEAKING AT THE OIL SCAVENGE LINE ADAPTER, WITH THREAD DAMAGE AT THE BOLT HOLES (2). OIL COOLER REPLACED AND AIRCRAFT RETURNED TO SERVICE.