During the approach to Topeka, the crew was unable to extend the left gear. The crew diverted to Kansas City, and after many unsuccessful attempts to lower the left gear elected to land wheels-up. The left main gear was jammed into the geardoors. The aft hinge bolt was missing from the left inboard gear door, allowing the gear door to shift just enough to jam the gear as it started to extend. Seventeen days prior to the accident, the loose aft hinge was noted during preflight. Company maintenance was unable to retorque the bolt due to the nutplate attachment rivets being stripped. This item was being carried as a delayed discrepancy. These parts can only be lubricated before installation. The entire assembly is almost impossible to inspect, remove, lubricate, install, torque, and safety. Replacement of the nutplate is considered a major undertaking. The manufacturer stated that "short cycling" the gear as many as 18 times would eventually break open the gear doors. This emergency method of extending the gear had not been disseminated to all operators.