I bought an old house with double-hung vinyl windows in which the sashes have yellowed considerably. 1. Can anyone suggest a good cleanser? 2. Ideally I would like to paint them to match the interior trim. Is this a good idea? What type of paint will stick best? What about the parts of the window that slide against each other (the face of the upper sash is rubbed when I raise & lower the lower sash)? I definitely won't paint the channels that the windwos slide in!