Oil leak not by the valve gasket it was coming from the exhaust manifold?

If you have oil leaking from the exhaust manifold, it may indicate a problem with the gasket or with the manifold itself. It's possible that the gasket wasn't properly installed when you changed the valve cover gasket and now it's causing oil to leak from the exhaust manifold.

If you loosened the exhaust manifold and oil started to run down the back of the engine, that could indicate a more serious issue such as a cracked head or a blown head gasket. A cracked head or blown head gasket can cause oil to leak into the combustion chamber, where it is burned and exits through the exhaust system.