I cleaned with a tissue and some pur based alcohol product. WD40 is fluid and doesnt clean that good as alcohol. When you do this use a product which evapored quickly. WD 40 doesnt do that and lays a layer on it. So something alcohol based will do. To undo the cover you have to use a bit, as you see in the picture still stuck there. Bcus that screw is hidden behind the wheel and there isnt a way to get the screwdriver in.