First of all, go ahead and take out your battery and inspect for rust-through at the firewall. (That should not be the problem unless the car has been really neglected.) You may as well clean the battery tray and if needed, repaint or treat with POR 15 while you have the battery out. Be very careful to not bump the heater control valve on the firewall while you are removing or installing the battery. It is pretty close quarters and they will break very easily when smacked by a 40 lb battery.

Back to your main question concerning the most likely path of a water leak into the passenger compartment...Leaks could have more than one cause but my bet is on front and/or rear windshield seals needing replacement.

Check these threads...

http://www.peachparts.com/shopforu...d.php?t=164755

http://www.peachparts.com/shopforu...d.php?t=164697

http://www.peachparts.com/shopforu...ad.php?t=64843

Also Note Murrow's suggestion to chase the sunroof drains with weed-eater string to clear them out and not damage the finish. (That is if you have a sunroof)

Hope this helps
Motor on

__________________
Bama1


2008 SLK 280, Firemist Red - "Hurricane"
2001 F150 Lariat 4x4, Black on Black - "Badboy"
1982 240D 4 speed survivor -"Pearl" - Donated to Vietnam Veterans
1962 Oldsmobile Dynamic 88 -"Gertrude"

1954 model original owner - ~2.5M
Gray softtop/solid exterior/modified chassis