Most of us have heard horror stories relating to hobbyists' experiences installing windshields and rear and side windows. Practically everyone knows someone who cracked a windshield attempting to install it. The stories are so common that many hobbyists simply won't try to do the work, and that's too bad. Windows are actually very easy to install as long as you don't make the fundamental mistake.
And what is that mistake, you might ask? It's applying too much bending force on the glass, causing it to break. In side windows (flat glass) the problem usually occurs when the chrome frame is being pressed onto the edge of the glass. In rear and front windows it happens when trying to force the assembly over the body flange. In all cases this is due to failing to lubricate the gasket that holds the glass in place.
We've found two "foolproof" ways of lubricating gaskets and both are inexpensive. For side windows the best lubricant is liquid detergent. It allows all the pieces to press together easily and can either be washed away or it dries up internally. For windshields and rear windows we rely on rubber grease. It allows the glass/rubber gasket sandwich to slide into the body channels smoothly without binding or forcing. It is weatherproof and eventually evaporates and doesn't mar any surfaces.
Rubber grease is available at most auto parts stores in the brake parts section. It's used to lubricate brake cylinder boots and piston O-rings before assembly.