Why do the replacement mufflers solve the problem? From your analysis the screws for them must be different and stretch less? Do they come with new screws, and can the screws be bought separately for use with the stock muffler? I have the 36 46 and 61 NT engines. The 61 NX engine differs from the 61 NT engine by only the head. I have tried to buy the NX head to upgrade my NT, but they are always backordered. Wonder why?

Thanks,

Sincerely,

Richard