Birddog,
What I use is an anti-seize compound. I just couldn't think of the proper name for it earlier. The tube I use has "NAPA" written all over it. I looked at it when I got home. It looks just like the stuff on the Rice breechplug. It should last forever because a little goes a looong way.
I agree in part about a breechplug being permanent. I especially agree concerning production guns like TC, Lyman and CVA. But when discussing gun building and custom barrels like Colrain, Green Mountain, LC Rice, Getz and others then they will be unbreeched, more than once. There are a couple of steps that are just done better with the plug out.
So, if the plug is coming out anyway, common sense tells us to be sure it will come out without hassle in the future. Especially after a lot of Blackpowder has been shot in the gun.
The Anti-seize is not to seal the threads or lock them in place, its to be sure the rifle can be unbreeched if needed anytime in the future.