Im having the exact same problem on my 02 wrx. I just rebuilt the engine and replaced all the hoses and clamps with new ones. I know the smell is not coming from the front of the car, and just like you I only smell it when the window is down. Im getting the same CEL "small leak in the evap system. Im pretty close to just pulling the tank and replacing all the hoses and clamps and probably both of the gaskets on the tank it self. It would be nice to hear how this thread ended before I go through all that work.