We had a Pella sliding door installed about ten years ago and never got around to staining or painting the interior frame (long story). Now that we are finally going to do it, how should I prepare the wood? Just scrub it so it is as clean as possible, or should I lightly sand it? It appears to be bare wood, but I don't want to destroy any sort of coating that it may have.

(I also posted this on the Furniture Forum, but I think this is probably a better fit)