Scrubbing was necessary to remove the build-up of oil and grease residue. Brass brushes work best and keep the surfaces original finish intact. Use the brass brush on all surfaces-cast iron, S/S, and aluminum-as it will not scratch like a steel brush. Scrub the area and reapply the cleaner until you see the original surface before rinsing. This takes plenty of time and patience, but is very rewarding when you see the difference. If the engine had been cleaned annually, this could have been avoided.