If you have ruled out the heater core as being the problem, the water leaking on the passenger side under the dash is caused by a faulty design of a rubber cover placed over the HVAC unit.
What you need to do is remove the cowl & then you will have access to the covering over the HVAC unit.
You can either construct a new covering or contact Chevrolet to see if they have a replacement one. Also, be sure to clean the area thoroughly & use a good waterproof sealer.
Wednesday, June 27th, 2012 AT 3:35 PM