Coolant leak from header bolt hole.

[Weasel Diesel]

I have a pair of World S/R heads. Now in the instructions, it says to use a thread sealer on exhaust bolts as the bolt holes intercept coolant passages on some of the holes..OK... I used Permatex liquid type with teflon...leaked,...tried the teflon pipe tape,...leaked. Is there any other sealers out there to use ? It stays good till it gets hot. I figure its melting the sealer being at the exhaustport. Think maybe a high temp RTV ? heck, I don't know, I'm disgusted. I am at the point of putting header studs in with JB Weld to stop it, but that's pretty drastic....HELP please. Called World,... they state the liquid stuff I used should seal it...it don't.