Coating the inside of repro mufflers. Why?

[Steverino]

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