Are people using a sealant for the manifold gasket?. How about on the exhaust manifold to exhaust? I'm using the factory metal gaskets.

For any gaskets on the head or block I've been using aviation sealant, for exhaust flanges I use high temp copper grease

Sure you can use sealant. Or not. I never do, and have never had a leak

I have always used either Loctite Master Gasket on the inlet and high temp rtv on the exhaust although lately been using the rtv on both.
I was told some time ago by a very good old school rally car builder that if you use a gasket and it blows you are out- rtv doesn't do that. The worst you may get would be a pinhole size leak.
Good preparation is no doubt the key to all this.
Interestingly enough my engine builder who specializes in Cosworth BDA engines only uses rtv ( silicon )on both manifolds and the finish record of cars that he prepares speaks for itself.
Cheers
Dave

Misleading. Are you all applying sealant between the manifold and gasket or between the gasket and head? Or both?

Between the manifolds and the head- in other words no gasket

RTV is a type of gasket. Often called "gasket maker". Nissan calls it "liquid gasket" and uses it on some engines including SR20