I also have a SMALL leak from my heater control valve. The water + antifreeze occasionaly drips down onto the trans hump and then onto the passenger side floor. If this is the problem
you should have some residue from the antifreeze when the water evaporates.
Ive had the seal on my windshield leak, too. The water would drip onto the inside of the dash and drip onto the floor or my legs as I was driving.
The holes in my kickpanels also let some water in but not enough to get me off my butt to plug them.
Lastly, the plasic that seals the doors, under the door panel, is there to keep water out. Mine are gone and when it rains i sometimes find water running down the door, just below the
door panel, onto the floor.
I hope this helps you track down the leak.