Improper inspection of the muffler assembly resulting in erosion going undetected and the rupture of the muffler and shroud while in cruise flight. The condition caused melting of portions of the air induction system, loss of engine power, and the pilot's attempted forced landing that resulted in collision with terrain that sheared one main landing gear and fractured the wheel of the other main landing gear. A factor in the accident was the pilot's obscured vision due to smoke in the cockpit.