What happened
While in cruise flight, the pilot observed that the left engine began to lose oil pressure. After receiving vectors to the nearest airport, the pilot noted that the left engine was running with increasing roughness. Consequently, the pilot shut down the left engine while on final approach for runway 3.
During the approach, the pilot realized that manual extension of the landing gear would be necessary. However, there was insufficient time to complete the manual extension, prompting the pilot to attempt a go-around. During this maneuver, the aircraft collided with the terrain past the runway.
The investigation
An inspection of the engine determined that the loss of oil occurred because the crankshaft oil seal had moved forward on the crankshaft and displaced from the crankcase bore. Further examination of the seal revealed that it was a 'lipped' seal, which was not an approved component for use with this specific crankcase.