Product to clean running boards

[msm]

The running boards on my X5 seem to be a bit tarnished/stained. I thought of polishing it with a metal polish, but it has little rubber grips along it, which I cannot seem to remove. I don't want to end up getting the metal all nice and clean, and then having the rubber grips look crap.

Below is a pic I've taken from elsewhere, but I have similar stains on my boards:

Any recommendations on what I can use on it, that will not damage the rubber studs, but still clean the boards.