What was found
SEA - LEFT GEAR DOOR LIGHT REMAINED ON WHEN THE LANDING GEAR WAS RETRACTED. DOOR VISUALLY INSPECTED AND VERFIED TO BE OPEN. WHEN GEAR CYCLED THE LIGHT WENT OUT. FERRIED AIRCRAFT FROM SEA TO PDX FOR REPAIRS. IN PDX, RIGGED THE ALTERNATE EXTENSION SYSTEM AND REPLACED THE HYDRAULIC MANIFOLD (S/N: 0040, TSN/CSN 28478/38930, TSR/CSR 12555/17633), AND THE MECHANICAL SEQUENCE VALVE. PERFORMED GEAR SWINGS AND TEST FLIGHT, BOTH SATISFACTORY. AIRCRAFT RETURNED TO SERVICE.