This is a known issue with Honda ATV's and it is still an issue to this day. On one of the parts that was used to repair my ATV the dealership noticed the same issue that is in the image, the threads on the inside of the engine where the oil drain plug threads in was split on the inside. Anything beyond 18ftlbs of torque can split the threads on the inside of the cast engine part and cause a part failure from chunks of aluminum bouncing around inside the engine.