Thoughts on gasket sealant

I'm getting ready to replace the water jacket cover on my 1976 Evinrude 9.9. I've been using emory paper taped to a slab of very flat marble to sand down the cover and the head in an attempt to make them perfectly flat. After quite a bit time at this, I can see that the faces are still not totally flat; the very top of the cover, and the very bottom of the head rise out of plane a small amount.

I'm interested in people's thoughts on gasket sealant. I was initially thinking of using Aviation Gasket sealant to dress the gasket. But because the thermostat is under the cover, I'm worried about the mess when it comes time to replace the thermostat.

If I don't use sealant, can I expect the cover to shape itself slightly to conform to minor variations in the faces of the cover and head? Will the gasket alone be enough to allow for these variations? Or is sealant the answer to a slightly out of plane face?

Any thoughts on whether I should stay away from sealant or not would be appreciated.

Thanks,
Jonathan

Re: Thoughts on gasket sealant

I've always used OMC Gasket Sealing Compond or Permatex #3.

Re: Thoughts on gasket sealant

Or you could use a thin smear of 3 bond sealant eg 1215 grey, or you could use hylomar jointing compound in a spray can. That is what i use.