No.
Blown head gasket and/or cracked head.
Most connections / joints between parts have a gasket to prevent leaks. So a failed gasket is a typical cause of leaks, including where the exhaust pipes connects to the exhaust manifold.
I think they both work pretty well. Don't usually have a choice about which, because the manifolds you have dictate which type of seal you'll use.
It seals the exhaust manifold to the cylinder head so it doesn't leak and is made of a high temp material.