Event
During a night flight, the pilot observed decreasing oil pressure on the right engine and diverted to a suitable airport for a precautionary landing. After receiving night vectors from air traffic control, the pilot arrived high on the final approach and obtained tower clearance for a descending 360-degree turn to lose altitude. While executing this turn, the right engine oil pressure dropped to zero, and the engine stopped. The pilot feathered the propeller and continued the approach.
Landing
The pilot became preoccupied with managing the single-engine operation and the approach path. This preoccupation caused the pilot to neglect lowering the landing gear. Consequently, the aircraft touched down with the gear retracted.
Investigation
Post-flight inspection revealed that the oil sump plug was missing from the right engine rear case accessory section. Additionally, resultant fuel exhaustion was noted.