i was winterizing my gasoline atomic 4 yesterday. i replaced all 4 spark plugs. 2 of them were all coated with a black powder. two of them were coated black but were wet. (oil?) not sure if this means anything. the engine runs fine and didn't have any trouble all summer. i looked in my moyer marine a4 manual but i didn't notice anything about dirty spark plugs. is this something i should be concerned with or is it just normal wear and tear.