I ran across this on Facebook from the CB72/77 UK club. One fellow was recommending spraying a very heavy coating of heat resistant paint down the throat of new repro muffs. Don't repro mufflers handle heat well? Do they turn blue easily? I don't Facebook well so I couldn't track down the beginning of the thread.
https://m.facebook.com/groups/745275825 ... 8396217756
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1965 Honda CP77 — Ulsan Metro City, Rep. Korea
Restored with original parts — Owner: J. Doe