When the landing gear was selected down the left main landing gear did not extend. All efforts to extend the gear were unsuccessful. When the aircraft was landed the left wing settled to the ground and the aircraft swung to the left. Preliminary investigations disclosed that the left main landing gear door had failed to open. Because the aircraft was new, having only been in operation for 330 hours, the manufacturer dispatched an investigation and repair team to assist the local maintenance organisation. It was found that the left main landing gear fuselage door up hook pivot had seized. The initial function of the gear down sequence is to release the hook to allow the door to open. With the hook seized the gear remained in the up and locked condition. The pivot pin and bush are both steel and were found corroded due to lack of lubrication. As well as the poor design of steel on steel, there was found to be no lubrication period or lubrication method detailed in the aircraft maintenance manual. The manufacturer's immediate action was carry out a fleet modification to remove all main landing gear doors except for the gear leg mounted door. Subsequent assessment has found the door pivot mechanism to be inadequate and a fixed landing gear fairing has been introduced on a fleet wide basis.