Hi Phil,
I blew both of my header gaskets out a year apart. Because mine are so hard to get at (FE), I decided I would try the copper gaskets rather than the composites. The RTV just won't work for me because of the tight working conditions - I would have that red gooey crap all over me and the motor (although I did use it on the collectors). They have been on a couple of years now and no issues. I tighten everything up twice a year just to be safe.
Good luck.
Phil
427 Roadster, #4279436
FE Specialties FE
3:31 and Toploader (wide ratio)
Roseville (N.Cal)