Hi Kirk,

My son had the same problem with his 2003 Cadillac Deville. After some homework I picked up a can of evaporator cleaner. The one I settled on comes with a tube where you insert the tube into the drain hose from the evaporator. You spray the foam and it fills the compartment that houses the evaporator, and once it's cleaned it drains itself back out of the drain hose.

I followed the instructions and one treatment significantly reduced the odor, and a second treatment eliminated it completely. It's been a couple of years now and the smell hasn't come back. Here's what I used.

LG_Kool-It-evaporator_sell-sheet6.pdf