Dead thread resurrection winner of the day (there's been a
lot of discussion since the original post 13 years ago).
IMHO the best way to fix a leaking windshield is to remove the glass for a couple of reasons. IME and others, you often find rust under the windshield gasket so the metal "frame" area should have the rust removed/killed and then repainted.
Also the windshield is not just sealed to the body, it's
glued to the body ie: the proper material is both an Adhesive and a Sealant, so roof sealer or RTV will not have the same properties as the correct windshield glass product.
Not knowing how the windshield was installed there's no way to say for certain where to put the sealant if you wanted to go that route (ie: between the rubber and glass, and the rubber and the body)
Try more searching for Windshield Leak Leaks and read through more of the previous threads, it's been discussed, a lot.
Some light reading: