On March 12, 2022, about 1245 central standard time, a Beech A36, N9410Q, was substantially damaged when it was involved in an accident near Heavener, Oklahoma. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the flight was from the Bentonville Municipal Airport/Louise M Thaden Field (VBT), Bentonville, Arkansas, to the Mena Intermountain Municipal Airport (MEZ), Mena, Arkansas. After beginning his descent into to the destination airport, he noticed a dramatic drop in oil pressure to 14 psi. He began to search for alternate airports since his destination was not reachable and the terrain was mountainous. He turned the airplane toward the west to attempt to reach the Robert S. Kerr Airport (KRKR), Poteau, Oklahoma, but within 1-2 minutes the oil pressure dropped to zero and the engine seized. The pilot executed a forced landing to a field. During the landing, the airplane struck fences and livestock feeding troughs, which resulted in substantial damage to the wings. Postaccident examination revealed that the engine No. 4 cylinder rocker cover was completely off, and the No. 6 cylinder rocker cover was only being held on by 4 bolts, all of which were very loose. The No. 4 cylinder rocker cover gasket was not located after the accident. The No. 4 cylinder rocker arm shaft bolt was missing. Multiple rocker cover bolt holes were elongated and embossed with the bolt thread pattern. Metal shavings were observed throughout the valve assembly area as well as deposited on the cowling and airplane along with the lost engine oil. Review of maintenance records revealed that the most recent maintenance on the engine was an oil change performed on December 22, 2021. The entry for the oil change noted that a post-maintenance engine run did not reveal any leaks and included no mention of work performed on the rocker covers. On November 17, 2021, an annual/100-hour inspection was performed on the engine. The entry for the inspection noted that a post-maintenance engine run was normal. A specific notation regarding leaks was not included in the endorsement. No mention of work performed on the rocker covers was noted. Further examination of the engine maintenance records showed that the engine had undergone an overhaul and was reinstalled on the airplane on November 2, 2016. Subsequent to the overhaul, several maintenance entries were made; however, none of the entries since the overhaul noted any work performed on the rocker covers of the engine. Interviews of personnel at the maintenance facility that performed the most recent overhaul revealed that approved hardware and gaskets were used to secure the rocker covers at the time of the overhaul. An interview of the mechanic that performed the most recent oil change revealed that he had not accessed the rocker covers and had no reason to while performing the oil change. Further attempts to discover when the rocker covers were last removed were unsuccessful.