Skeleton of Front Dash Pictures ?

[xnamerxx]

The AC enters the car directly in the center of the firewall. You can see it from the engine bay there are two metal lines that come out of a large rectangular grommet. The heater core is directly to the right of that in a smaller hole with two black hoses coming out of it. It would be really obvious if there was damage in either of those from the firewall. You can see both of those holes from the picture Jason has posted neither one should allow enough of an opening for a squirrel or rat to get in. In order for there to be a breach in the cabin air filter it would need to get past the blower, which is a pretty tight space. There is a small hole where the water drain is located, in the passenger side footwell, you can also see the hole in Jason's picture.

I would be more willing to bet that the holes that are plugged with the large rubber grommets on the underside of the car, is where its getting in rather than from the firewall area. There are 4 in the cabin area and one large one in the trunk. I would be looking there.