[truckster]

I always use glass cleaner to lubricate rubber seals. It wipes right off, so cleanup is easy.

Only use urethane if you don't plan to re-use the gasket in the future. Urethane is a glue, and it tends to tear the gasket when you attempt to remove it. And don't ever, ever use silicone on automotive glass. I can't tell you how many times I've tried to reseal a windshield someone used silicone on, and every trace of it has to be gone before the windshield can be resealed. The flow-grade butyl that Grumpy recommends is the right stuff. You don't need to do the whole windshield, either, just 12" in from each corner, between the rubber and the steel. Go down the edge about 4" and you should be good to go. That's the way the factory assembly manual recommends and that's how I always did it in my glass shop.

Pro tip: Have at least one helper, and start installing the windshield from the top. Once you get the top corners in, the rest of it is easy. Also make sure you have a hook tool to help pull the rubber over the pinchweld if it gets stuck.