James "Doc" Lewis has been "messin about in boats" for as long as he can remember. He is owner/operator of BoatDocs1, a full-service boat detailing-yacht maintenance business serving the Emerald Coast region of Florida. To learn more about boats and keeping them looking their best visit his web site at: http://www.boatdocs1.com/
NEVER use any kind of regular window cleaners, detergents, abrasives, petroleum based products, or alcohol on vinyl windows. They are too harsh and will damage the top coat, speeding up the loss of plasticizers. The vinyl will dry out, turn yellow and brittle, and soon need to be replaced. You've seen this before, now you know why.
Right along with this is a big ditto for all of your vinyl products either on the boat or ashore. Only the mildest soap solution, complete rinsing and a safe protective coating will keep all of your vinyl goods looking like new.