Art,
Jeff is not kidding and I have no clue why Prevost has not made one of their vendors resolve the problem.
Maybe if enough of their technicians complain you might actually get a gasket and windshield that will actually fit as they should, but just be aware if this age old problem still exists you are not going to have an easy job putting the windshield back in with new gaskets.
As a side note, there should be no additional sealer used when a windshield is installed correctly. The key appears to be to avoid pulling on the rubber insert as it is being installed into the groove in the gasket. If it is stretched, it is also smaller in cross section, and thus will not fit tightly in the groove and make a complete seal between the gasket and window frame or gasket and glass.
Under normal circumstances with lubricant on the gasket and glass and an insertion tool for the rubber insert it is not unusual for the glass to go in and out in 20 minutes. We used to teach folks at rallies how to replace glass and even those that had no experience at all were doing their first replacement in 30 to 45 minutes. But not with new gaskets.