Rear Window Rubber Installation Tips:Fit your new window rubber to your cab first, then install the window glass.Use a rubber friendly lubricant such as WD40 and the Windshield Stick (#38-0796) to ease installation and avoid damaging your window rubber.Window rubber shrinks; your new window rubber may appear slightly larger than the original prior to installation.Standard Rubber Seals do not have a groove for trim.Custom Rubber Seals do have a groove for trim.