My one piece RV windshield leaked in a couple of areas driving in the rain at highway speeds. It wasn't easy to find but it turned out to be leaking between the glass and the rubber seal it sits in. I pulled the spacer strip out of the groove on the outside of the rubber seal, pulled the seal up enough to apply some non silicon window caulking between the glass and the rubber seal. This did not work at all, the first time driving at 60 mph in rain it still seeped in between the rubber seal and the glass. Googling more found recommendations to use red rubber grease between rubber and glass. So I cleaned out all the caulking and smeared in the red rubber grease. One year later and no leaks.
It's hard to find , mostly available in the UK. I used Millars Oils version but also available from Sealey
http://www.thelastgreatadventure.com/archives/2018/02/looking-after-your-rubber-with-red-rubber-grease/
