The aircraft made a forced landing in a pasture and collided with a cow after the engine quit. The pilot said he has noticed the landing gear in transit light come on at about 10 minute intervals during the flight. He said he had noticed a red fluid dripping from the bottom of the right wing during his preflight. At destination, the landing gear would not extend. The in transit light came on but the gear down indication did not activate. He said he tried to activate the emergency extension system but could not open the cover. He made a radio call in an attempt to get help on how to open the emergency gear extension valve cover. While circling, the aircraft ran out of gas. Post accident examination showed a leak in the right gear actuator. The hydraulic reservoir was almost empty. The pump was unable to build up pressure to extend the gear. The 'O' ring was unseated in the right actuator. The emergency cover was opened without difficulty after the accident.