A lot of big trucks still use a rubber gasket. Anybody that installs auto glass should know how to install the glass with a rubber gasket, but some are more skilled at it then others. If your talking with a glass company that doesn't like to deal with the rubber, go find a different shop, they are trying to tell you they don't know what they are doing. My new glass guy guarantees a no leak with rubber gasket, the last shop wouldn't do such a thing, and nearly every window with a rubber gasket he did leaked. Gene