Re: Water enters near heater core at Car Wash!
Are you sure the water is coming in from the underside?
I haven't heard of that one before, and can't think of where the water would be getting access...
What is a little more common is in the winter for the drain tubes of the sun roof to become clogged with ice, and then when the car wash sprays the TOP of the vehicle and water enters through the sunroof, with the drain tubes clogged it leaks down the A-Pillar and eventually ends up behind the dash. Not saying that's what your problem is though...