2003 c240. The lower vent (under the dash, by your feet) won't close. So, I get less then full full air from the front vents etc. Read a few threads on this. Sounds like I need new diaphrams, or the pods are bad. I'm a pretty good DIY er, but I really don't know where to start. Don't want to just start tearing the dash apart. Anyone have a "how to" guide on this. Thanks.