1980 280zx I'm installing a new Intake/exhaust gasket, the manual doesnt say anything about using any type of gasket sealer on the gasket. What do you think?

You don't need to use any sealer. Just be sure to purchase a top quaulity gasket that is thick enough. Also, be sure to recheck the fasteners torque after the engine has run for a day or two. If your mounting studs look questionable, now is the time to replace them.