I stand corrected. That's what happens when you only skim over a post. Certainly if Weil McLain states that it's OK to use then it most certainly is.
I actually installed a Weil McLain boiler about 25 years ago in my old house and I one time had to get into the flue box by removing the cover. At that time they specifically mentioned high temp RTV. I believe it was Dow Corning 736 that they recommended?
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