I scratch my intake manifold a little not bad just a little scratch and there gasket material left over that I can't scrap of with any plastic. Should I use sand paper to remove the remains material and smooth out the surface?
Use a putty knife flat at an angle never the corner of. Only deep gouges to worry about would be if it was from intake passage to the outer edge. Across the surface not so much, can fill with silicone sealer and wipe excess off.