interior leak!!!

ok so im redoing my interior and am trying to take care of any leaks before i install it. i went over the front of the car today with a hose, and was surprised at what i found. there was a small leak from the drivers side that i caulked up, and another where there is a plastic plug that goes to the firewall. but the real problem is on the passenger side. i let the hose run for a minute or so when water started flooding in under the dash. i felt around because i couldnt see, and found out it is coming in through the a/c box (not sure of the real name) . its leaking through the seam where the upper and lower parts of the a/c box go together on the passenger side right by the vacuum valve that is right there. anyone know what seal is bad and what its gonna take to fix??


thanks for the help