After selecting gear up on DEPARTURE, the pilot noticed the gear unsafe light did not go out. He assessed that it was probably a false indication and continued with the local flight. On return for landing, the right main landing gear leg would not extend by the normal or the emergency systems. The pilot elected to land with the landing gear retracted. After conducting a trial approach and overshoot on runway 31, he made a shallow approach for the same runway from 6 to 7 km out. The wind was from the north-west at 10 to 15 kts. His intention was to touch down near the threshold. Full flap was selected on long final and airspeed was reduced to 60 kts, 15 kts below the normal approach speed. On late final sudden sink was experienced and the aircraft struck the ground about 120 m short of the runway. It then slid into a large drainage ditch along the airfield boundary. The right landing gear leg failed to extend because the bolt joining the upper and lower torque links had fractured. This bolt had become corroded and seized in the bushes through lack of lubrication. Bolt failure allowed the upper torque link to catch on a section of the landing gear bay, thereby preventing the gear leg from being extended. The pilot indicated that he elected to conduct the approach at a lower than normal airspeed because he wished to minimise the resulting ground slide.