Well, since I have never not used sealant, I don't know if I am the best guy to ask. I can say I have never had any leakers and many of the guys I have helped fix leakers didn't use sealant . . . "with new rubber"
Also the way to apply sealer is to use a small squirt can made for specifically for applying automotive sealer. Looks like a small trigger pump oiler can only the spout has a flat / slotted outlet. Hard to explain, I'll see if I can get a picture of one and link to it.
Look at item
"Q" . . . you apply the sealer (buy the flowable stuff) AFTER the windshield is installed. Ken
