I never trusted Permatex to survive 1600+ degree heat. All kinds of gaskets from cheapies to soft copper were used on the hot rod but they always leaked. I never split the flange on these like I did on my last headers.
Spliiting the old header flanges made it harder to install the headers due to the flex and they still leaked.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon