Now brush in black Kiwi shoe polish very liberally. The kind in the flat can.
Hmmmm, this sounds like a scene from the movie, "World's Fastest Indian", about another Kiwi, Burt Munro. Burt supposedly used shoe polish to get his old tires past the tech inspectors. I really enjoyed that movie.
Should be a lot safer to use on running boards.
Ditto on the shoe polish. gives nice luster and doesn't collect dirt.Soap & water scrubbing brush let dry. Now brush in black Kiwi shoe polish very liberally. Thy kind in the flat can. Let it soak in & dry then polish off with a soft brush & rags.