On October 26, 1995, at 1610 hours mountain standard time, a Great Lakes 2T-1A-2, N3808F, nosed over while making a forced landing 4.5 miles southeast of Chandler Airport, Chandler, Arizona. The aircraft sustained substantial damage and the commercial pilot was not injured. The aircraft was operated by Chandler Air Service, Inc., and was rented by the pilot for a personal flight when the accident occurred. The local area flight originated from Chandler Airport at 1545. Visual meteorological conditions prevailed at the time and no flight plan had been filed. The pilot reported that the purpose of the flight was to practice an aerobatic sequence three or four times and return to Chandler. However, at completion of the first sequence he felt an abnormal vibration in the engine and terminated his practice. The engine rpm was 200 rpm low and could not be restored with the propeller control, and within a minute engine oil began to appear on the windshield. He turned toward Chandler when the pilot of a nearby aircraft radioed that he was trailing smoke. The pilot identified a suitable dirt road and decided to make a precautionary off-airport landing. During the landing rollout, the aircraft struck a ditch and nosed over. Examination of the aircraft revealed that the engine oil supply had vented overboard through the engine crankcase breather and the propeller shaft. There was engine oil on the exterior of the aircraft aft of the breather tube, and on the exterior of the engine aft of the propeller shaft. The propeller shaft seal was displaced from its normal position and was positioned onto the propeller shaft. The engine had been overhauled by the operator 11 hours prior to the accident. Disassembly of the engine by the operator following the accident revealed that the intake manifold tube flange and flange gasket (Lycoming part numbers 70485 and 71973) on the number four cylinder were leaking due to misalignment. A hole had burned through the number four piston. The hole was located in the perimeter of the piston around the rings and went through to the crankcase side of the piston in vicinity of the wrist pin.