If it is the windshield it is a known issue with Winnebago coaches.
The windshield is bonded to a steel frame. The rubber around the windshield is primarily cosmetic but should keep water away from the frame to some degree.
If water gets to the metal frame it can rust and push the windshield out enough to cause leaks and/or crack the windshield.
My passenger side cracked and the driver side leaked and cracked. I had both replaced at the factory (about three years apart)and asked them to clean and rustproof the frame. My insurance covered it although I had to pay a deductible.
Last summer the drivers side had to be replaced again due to a rock causing a crack. The tech said the frame looked good now - no rust.