I've installed windscreen/windshields a few times and never used a sealant on the rubber to body junction, however I had a fair amount of rust repaired on the flange where the rubber sits and have read the rubber traps water. The Brits over at TMF are all over the place in regards to using a sealant. I'm thinking of using a flexible windscreen sealant like this:
CRL Black Windshield Sealant (https://www.dkhardware.com/black-windshield-sealant-7711-product-27087.html?)
What's the general consensus? "To goo or not to goo" that is the question.
I've never used any. If you're driving a lot in rain, I could see where maybe a little something is a good thing. I've done a ton of windscreens on my cars and no rust issues under the rubber.
They used something similar when they installed the windshield in my Jag, but we didn't when we put the glass in my Mini and I haven't had an issue. Don OTOH, his Pup leaked like a sieve after Safelight did his, he took it back and they used sealer on it and that seemed to take care of it.
My feeling is it probably doesn't need it if done right, but what can it hurt?