With my Walker trufit muffler starting to go on me with only 4 years of service, can anyone tell me what kind of steel is in the mufflers that the car manufacturer's installed on the cars when new. Those original mufflers seemed to last alot more longer than these aftermarket OEM fit ones made of aluminized steel. Also does anyone know if Bosal mufflers are better? I'd like a muffler that doesn't need replacing ever 3 to 4 years so any suggestions before I purchase a replacement will be appreciated.