Thanks Meisermind! I tore everything down to the heater/ evap core, but when I pulled off the cover I noticed that there was some yellow greasy liquid on the bottom (where there is a drain hole). Parts of the heater core and surrounds were noticable damp with the same greasy yellow stuff. Does anyone have any idea what this could be? I am somewhat sceptical about it being coolant as is is yellow and greasy and not green and watery. Could it be air conditioning related?