Here's how I think it is done, give or take, I could be wrong. Yes sealant is needed, some swear by
1. Tape up anything that you don't want sealant on
2. Put bedding/glazing compound into the pinch weld groove side of the gasket and then put it on the car and tape it so that it stays put on the pinch weld
3. Run a small rope on the inside of the gasket where the glass will seat, like 1/4" nylon rope
4. Place glass on to gasket and car and start working in the edge where your two ends of rope come together I think starting at the bottom works best
5. Get a plastic glass stick to help you work the glass into the gasket
6. As your working it in, you'll need to somewhat firmly smack the glass with the palm of your hand to get it to seat, now is a good time to say a prayer
7. Hopefully as you're pulling the rope along the gasket behaves and the glass goes into the groove
8. Before locking the bead down once the glass is set and the rope is out of the way, run the glazing caulk tube up under the gasket and glass and run a bead all the way around
9. Clean up all the glazing compound on the glass and lock the bead
10. Let it sit for awhile, and then run a sprinkler on it and pray that it doesn't leak before putting any trim on
BTW, that's 3M 8509, can be found at most paint supply houses or online.
