The aircraft underwent a 100 hourly inspection six days prior to the accident. During that inspection three oil leaks were rectified. When the aircraft commenced operations again after the 100 hourly inspection, the engine again started to leak oil at a significant rate. The operation was remote from the maintenance organisation. The pilot did not determine the source of the oil leak nor monitor the oil consumption rate during the days prior to the accident. On the day of the accident the pilot had been spreading superphosphate since late morning. He had finished that task and had commenced spreading clover seed. On the second seeding sortie he sensed a loss of performance. He pushed the throttle lever forward but the engine did not respond. He checked the RPM and noted it was 2200 and decreasing. He then noted that the oil pressure was indicating zero. At this stage he was about 50 feet above the ground and operating in mountainous terrain. He turned the aircraft to the right to avoid an area of trees and try to land on a steep upslope. The aircraft stalled into the upslope and came to rest after a 25 metre ground-slide. The investigation revealed that the oil filter bolt and sleeve had failed as a result of high cycle low stress fatigue. This was consistent with the retaining bolt being under-torqued. This resulted in the oil filter separating from the engine, a consequent loss of engine oil and finally, loss of engine power.