The rubber gasket around my one-piece windshield wasn't very old when deterioration at its top became evident. This was after Monaco Harrisburg replaced the factory windshield that had cracked from a bad install. There were a couple of gaps, one at the top and a pucker down the drivers side. I easily managed to work the side gap back into place on the cap, but the rubber is shot in a long strip at the top, with a lot of cracking. My electrical bay filled with water with heavy rains, and the windshield appeared to be the only obvious source. There is a large loom of wires descending through the bay ceiling, and gray foam was used to fill the hole. Last fall I finally found a fine drop of water on the foam plug, so that's the entry point, probably traveling down the drivers windshield post.
Last year Gerald brought a new silicone-like sealant to our attention, called Lexel. I located some at an Ace Hardware store and used it to stuff some of the gaps and rubber cracks along the windshield top. The water in the bay still shows up over time, but not as quickly. Admittedly I didn't catch both sides of the windshield top, and the passenger side has some micro cracking in the rubber that I could have addressed.
I can highly recommend the Lexel as it is easier to use than silicone and apparently more effective, esp. in the application, adhesion, and curative depts. A big thumbs up to Gerald for the heads up. This spring we hope to get into Beaver Coach Sales for a more permanent windshield fix and bay leak check.
Joel