I'm thinking that the rubber gasket is a fairly common item. When we replaced windshield on my '78 we had to trim the aluminum to get it to fit. Before we trimmed it, the glass would not set in "flush" with the body.
I had a local RV repair shop install the windshields on my '93. I thought they Glued the whole perimeter of the seal/body junction because they wanted the coach to set for at least 24 hrs after they installed so that it could cure.
When it comes to glueing or not...The classic coaches aluminum body surrounds the windshield thus transferring twisting torque to that area. I think that is less of a concern on the newer coaches with 100% composite type front caps.
Richard....I mean NO offence but I'm wondering if the seal is installed properly on your coach. I dont think that an annual "rework" on it should be necessary.
Remember that in a collision the windshield may be all that is keeping us in that coach. A few years ago we had a fatality not far from my house when someone went through a dislodged windshield of a tour bus during a collision.
These guys may be able to help find the proper rubber gasket:
http://www.steelerubber.com/