On arrival at the destination aerodrome, the pilot was unable to obtain a down and locked indication for the landing gear. He noted that when the gear was selected, there was an abnormal noise, and the gear motor only ran for a few seconds. On a subsequent re-cycling, a down and locked indication was obtained, but the pilot noticed a strong smell of hydraulic fluid. A diversion to a more suitable aerodrome was made, where a flypast confirmed that the gear appeared to be extended. The gear warning horn did not sound when the throttles were closed. However, the pilot was unable to move the emergency gear handle from its stowed position when he decided to use this device to ensure the gear was in fact down. During the ground roll, following a smooth touchdown, the right main gear collapsed. The investigation revealed that the right gear up-lock roller was seized. The pilot did not detect this fault during the pre-flight inspection. The landing gear braze rod, the push rod between the actuator and landing gear, was bent and the relevant gear position microswitch was incorrectly adjusted, resulting in a premature landing gear down and locked indication. The landing gear manual extension handle could not be moved because of an incorrectly fitted trim panel. All these mechanical defects were a consequence of inadequate maintenance.