Well first off, is your car a Targa or Coupe?
Since you said the words "911" and "leaks" in the same sentence, I'm going to assume you have a Targa for now.
The good news: Your not alone.
The bad news: There are about a bizillion places on targas to leak.
The best way to pin point leaks of this sort i to get yourself an assistant who will sit in the car (windows up) and watch while you use a garden hose to gently pour water over the car.
Be methodic; work slow. Start at the lowest point (like at the base of the windshield) and work up (the wing window seal). Hold the water over one section for at least a few minutes and wait for a reaction....don't go too fast.
At some point, you'll start to see the drip. Hopefully that will help a bit.
A few common places are at the bottom corners of the windshield (the seal shrinks with age), the top of the windshield to targa top seal (If water gets behind it, it can travel down the sides and into your cabin).
And the biggie is where the vent window, targa top, and windshield corner all meet...this seemsto be the hardest part on Targas to seal.
new seals, plenty of glue, and allot of patience are just about your only hope.
...hope you don't have a coupe.
Good luck,