no no no
the best thing you can do with that silly cone is walk to the bow and throw it as hard as you can. it has no place on the yamaha.
its really not even good to seal the transom mounting bolts.
if you have to use something then BRP gsketmaker or quicksilver perfect seal will work. but the OEM gaskets come with a heat activated sealer already on the gasket.
biggest thing is surface cleanliness NO WIRE BRUSHES, and surface flatness. it MUST be checked.
why are you trying so hard to re-engineer a decent product ?