Not many answers, so I dug around a little. Couldn't find much. Might only need to replace gasket? which would lower cost a lot.
http://www.atwoodmobile.com/images/windows.pdfhttp://www.parkin-acc.com/page51.htmlhere is a old, old posting with contact info. Maybe still in use?
http://forums.goodsamclub.com/Index.cfm/fuseaction/thread/tid/23081828/print/true.cfmI know what a hassle windows can be. Maybe you could make phone contact explain problem and then maybe e-mail in pic's to see what they recommend. Hope this helps.