It is just a suggestion from the FAA, not an order, but you probably ought to replace mufflers that have been in service for 1,000 hours or more. A university study shows older mufflers are involved in a high percentage of accidents related to carbon monoxide (CO) poisoning.
The FAA tasked Wichita State University to study the matter. The report shows that in carbon monoxide-related cases where the muffler was identified as the source of the CO leakage, 92 percent of the aircraft had a muffler with more than 1,000 hours of service.
The suggestion is contained in a May 7 special airworthiness information bulletin (SAIB). When developing the SAIB, the FAA considered the NTSB investigation of an accident on Dec. 17, 2000, in which a Beech Model BE-23 aircraft crashed, killing the commercial-rated pilot, the sole occupant of the airplane. The NTSB determined the probable cause of the accident was in part “the pilot’s incapacitation due to carbon monoxide (CO) and a fractured muffler.”