water leakage

I have a 91 grand am with water leaking into passenger compartment, especially the drivers side. All drain holes are clear and I have sealed around the vent cowling on the passenger side. My mechanic has run water over windshield and over the hood and couldn't find any leaking water. I would welcome any suggestions because when it rains I get 1 to 2 inches of water on the floor. HELP

Water leaking was on a TSB (Time Service Bulletin) for my car, 2002 GA GT, and the dealer said the way they check it is my pulling up the carpet and using a pressure washer to find the leak. Of course, someone has to be upside down looking up under the dash and anywhere they can see to find the leak. I'll have to leave it there for a while for them to check. Lucky for me it's still under the bumper to bumper warrenty. She told me she has seen them come in with a lake inside the car. Mine just gets the passangers side wet.