What was found
ON APPROACH, LOWERED LANDING GEAR AND NO AUDIBLE SOUND HEARD NOR ANY LIGHTS INDICATED IN GEAR HANDLE OR ON POSITION LIGHTS. FLAPS LOWERED TO FULL POSITION IN ORDER TO CONFIRM ABNORMAL INDICATION. LANDING GEAR HORN SOUNDED INDICATING GEAR WAS NOT IN DOWN POSITION. WHILE COMPLETING ABNORMAL CHECKLIST NOTED LANDING GEAR C/B WAS POPPED. CHOSE TO DIVERT BACK TO BASE AIRPORT. ON APPROACH, EMERGENCY DECLARED, ABNORMAL CHECKLIST REVIEWED, LANDING GEAR MANUALLY LOWERED AND CORRECT GEAR DOWN/LOCKED INDICATION OBTAINED. GEAR VISUALLY CONFIRMED DOWN BY TOWER. MAINTENANCE FOUND VALVE ASSY ON ACCUMULATOR LEAKING AT BASE. REMOVED/REPLACED VALVE ASSY AND SERVICED ACCUMULATOR.