I installed auto glass for 15 years.
Make sure the vent channel is clean and clear of rust. If you just painted it, wait for it to be completely dry. Use 1/4 X 1/8 rectangular butyl tape to form an adhesive strip within the vent channel.
While we would use automotive urethane adhesive for the finger bead seal, RTV would work [although the gasses from curing may encourage rust, and the silicone would pollute the surface for other adhesives}
Apply a fine bead of sealant and dress with a single edge razor blade. If you simply bevel the edge with the razor and leave the excess on the glass, you can come back after it cures and slice it off easily. Wipe any sealant off the channel while raw.
