I’ve cleaned a test panel with Murphy’s Oil Soap twice now and it still is not entirely clean yet. Are there any products or techniques that will help us wash away 30+ years of dirt and oils? I would like to be able to clean it all down to the DuPont sealer that was used back in ‘87 before deciding what to do next.

I am tempted to try Simple Green or a citrus type cleaner, but don’t want to do any damage by being hasty.