Well, I do not recommend reusing old gaskets, especially the head gasket. I would use some light sealer, such as the OMC/merc gasket sealer on most gaskets for sure. The only exception are the intake gaskets, no sealer should be used on those. But, I often coat those gaskets with some grease during installation.
I know that there are many recommendations about not using the light gasket sealer. On a new engine, with nice/flat machined surfaces, this is fine. But, we are working on old engines, most of the surfaces are not completely flat.
