I have had my Hemi car for 33 years, and the right side exhaust manifold still likes to leak for a few minutes on a cold start up.
I tried header gaskets and also Chryslers OEM gaskets with no real luck.
The only thing that "slowed" the leaking down a bit was using a thin layer of Permatex Ultra-Copper RTV along with the gasket.
It's almost livable now!