That's great you found it, definately look at the A/C lines going into the firewall also. They are on the passenger's side and look at the rubber seals around the lines, especially the small line. It should be a snug fit, you can check with a paper clip and see if you can easily fit between the copper and the grommet, if so water will get in. I would seal it anyway, you can use any of the automotive silicone sealers but not gasket makers. Good luck.