Unless a manifold gasket also seals coolant, such as the end ports on a small block V8, using any kind of sealer isn't a good idea. If the manifold and head surfaces are straight and clean using sealer is just a waste of time, and might allow the gasket to creep out of alignment. Having the alignment rings in place and the proper thickness so they don't keep the manifold from pulling up snug against the head is far more important than sealer.

The rule of thumb that I was taught to observe was to never use sealer on a gasket that is exposed to intake manifold vacuum. It's worked well for me for 60+ years.
Jerry

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