On January 4, 2017, about 1545 central standard time, a Mooney M20K airplane, N1159G, conducted a forced landing near Nacogdoches, Texas. The private rated pilot sustained minor injuries and the airplane was substantially damaged. The airplane was registered to and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan. The flight departed the Kerrville Municipal Airport and was about to land at the A L Mangham Jr Regional Airport (OCH), Nacogdoches, Texas.The airplane had recently undergone an annual inspection and the flight was the second flight since the inspection. The pilot reported that the preflight and flight was uneventful until he entered the pattern to land at OCH. The pilot prepared the airplane to land using the manufacturer's checklist, which included changing to the fullest fuel tank, which was the left fuel tank, setting flaps to 5° and lowering the landing gear. While on an extended downwind leg, the pilot noticed that his altitude dropped to 700 to 800 ft above ground level, so he added engine power to climb back to pattern altitude. The airplane's engine stopped producing power without any vibrations or sputtering. The pilot turned the airplane towards the runway and estimated the distance to be more than 1.5 miles from the end of the runway. He set up best glide but perceived that the airplane was descending too quickly to make the runway. The pilot performed a forced landing to a field but landed short in a wooded area. The airplane was moved to a secure location and several engine runs were conducted. Testing included scenarios with the fuel lines not purged of air. Engine runs with the left fuel line not purged of air, the engine would stop producing power if the pilot did not intervene and either activate the boost pump or switch back to the right tank. Testing found that when purged of air, the engine operated normally. Examination of the airframe found no anomalies. Examination of the fuel selector found no anomalies and each switch position was easily discerned. The mechanic, who has worked on Mooney airplanes for 48 years, provided a statement concerning the work performed on the airplane prior to the accident. During N1159G's annual inspection, a discrepancy found were numerous fuel stains throughout the belly panels. The source of the leak was determined to be the o-rings on fittings in the fuel selector valve. The mechanic was familiar with the fuel selector valve and suspected that the o-rings were deteriorated. To perform the required replacement, both fuel tanks were drained and the fuel selector valve was removed from the airplane. The fuel selector was not disassembled and the four unions were removed. The O-rings were replaced and the fittings were torqued. The selector valve was reinstalled and the fuel tanks were refilled with the fuel that had been previously removed and filtered. The fuel selector was moved from the off position to the left position and the fuel supply to the valve was purged of air thru the gascolator drain valve. The selector was then moved to the right position and the right fuel line to the selector was purged of air thru the gascolator drain valve. Inspection showed no leaks and after several days was re-examined and found not leaking. The annual inspection and repairs were completed. The mechanic, who is also a pilot, performed a post maintenance flight that included selecting both the left and right tanks during the preflight, taxi, and flight portions. He did not detect any leaks during the post flight inspection. The pilot has owned N1159G for almost 25 years and has at least 941 hours in the airplane without a similar incident occurring.