On October 12, 1996, at 1240 hours Pacific daylight time, a Cessna 182A, N4924D, made an emergency landing about 1 1/2 miles southwest of Agua Dulce Airport, Agua Dulce, California. The emergency landing was precipitated by a total loss of engine power. The pilot was conducting an instrument flight rules personal flight to Torrance Airport, Torrance, California. The airplane, registered to and operated by a private individual, sustained substantial damage. The certificated private pilot and his three passengers sustained minor injuries. Visual meteorological conditions prevailed. The flight originated at Wilton, California, at 0945. The pilot reported that on the evening before the accident, he flew to Mather airport, about 15 nautical miles south of Wilton. After arriving at the airport, he practiced some night instrument approaches with his flight instructor. At the completion of the flight lesson, the pilot refueled the airplane and returned to Wilton. The flight instructyor confirmed that the pilot refuled the airplane after the flight lesson. During the preflight on the morning of the accident, the pilot said that the right fuel cap did not appear to ". . . fit right . . . ." He said that the airplane was equipped with a Shadin Fuel Analyzer. He said that he monitored the Shadin gauge because " . . . the fuel gage seemed to be inoperative . . . ." About 2 1/2 hours into the flight, the pilot began a descent from 11,000 feet mean sea level (msl) to 9,000 feel msl. During the descent the engine sustained a total loss of power. He said that the Shadin gauge showed that there was 1.54 hours of fuel remaining. The pilot attempted to restart the engine, but without success. The FAA, Southern California Approach Control (SoCal) sector controller vectored the aircraft toward Aqua Dulce airport. The pilot, however, did not see the airport and elected to land on a road. A main landing gear collapsed during the emergency landing. After extricating his family from the airplane, the pilot said that he saw ". . . blue streaks on the passenger wing . . . ." A Los Angeles Sheriff's Department deputy reported that the fuel tanks did not contain any fuel. He said that the fuel tanks were not damaged during the landing; he also said that there was no evidence of any fuel siphoning from the tanks or engine compartment. Safety Board investigators examined the airplane at Aircraft Recovery Service, Compton, California, on December 10, 1996. The examination revealed several brown/orange streaks emanating from and surrounding the left wing fuel cap area. The right wing was not streaked. Investigators pour blue colored 100-octane fuel outboard of the left wing fuel cap. The fuel stain changed color to a light orange/brown color. Safety Board investigators filled the tank with water and pressurized it. Water leaked from the fuel cap area. Examination of the fuel cap revealed that the seal gasket was brittle. Investigators installed the right wing fuel cap on the left wing fuel tank. Water did not leak from the tank with the right wing fuel cap installed. Fuel cap leakage is addressed by airworthiness directive (AD) 83-13-01, issued on August 1, 1983. The operator is required to accomplish the airworthiness directive every 12 calendar months. The maintenance logbook examination disclosed that AD 83-13-01 was accomplished on August 11, 1996, during the annual inspection. At the time of the accident the airplane accrued 33 hours since the annual inspection was accomplished.