And now that you've read Alan's remedy, you too can be amazed that the combination of the bottom aluminum piece on cowl, the windshield and the big rubber gasket, all by themselves, is next to useless in keeping water where it belongs, on the outside of the car.
Do all that Alan says and it'll be tight and not leak. Don't do it ALL and your windshield will be as water-tight as a sieve.
Oh! And find my write-up on installing a windshield in the resources/knowledge section. Lots of tips from Alan and me and others to help with a successful install. Just don't crank everything up too tight!