On July 1, 1995, at 0750 hours Pacific daylight time, a Cessna 401A, N444RJ, sustained a left main landing gear collapse while taxiing for departure at Van Nuys, California. The aircraft was owned and operated by the pilot, and was beginning a cross-country flight to Cabo San Lucas, Mexico. Visual meteorological conditions prevailed at the time. The aircraft incurred substantial damage to the left wing, left wing tip fuel tank, and the associated engine and propeller. Neither the certificated private pilot nor his four passengers were injured. According to the pilot's statement and witness observations, the aircraft was making a right-hand turn in the run-up area at a slow speed when the left main landing gear collapsed. The side brace for the main landing gear is attached to a casting, which in turn is bolted to the inboard wing rib in the landing gear wheel well. Examination of the aircraft by an FAA airworthiness inspector revealed that the wing rib web cracked around the casting, which allowed the side brace to move and the landing gear to collapse. The inspector reported that portions of the crack appeared discolored and old. Review of the aircraft maintenance records revealed no history of landing gear damage or hard landing related maintenance activity. The aircraft was last inspected during an annual inspection 7 months and 60 flight hours prior to the accident. Cessna Aircraft Company was contacted for information regarding known wing rib web failures. Cessna stated that there are no known total landing gear collapse incidents due to cracks in the wing rib web. The company reported that in response to cracks found on the inboard wing rib web around the side brace fitting, Service Letter ME76-2 was issued on January 5, 1976. The letter details the installation of a steel reinforcement/doubler plate on the wing rib web behind the landing gear side brace fitting. Inspection of the aircraft revealed that Service Letter ME76-2 was not accomplished.