Has any one had a leaking firewall in there 93 gran am. I get water inside my car from the firewall. It seems to leak at the seam at the firewall half way down. We have found a rotten spot there and have filled it with fiberglass but that has not solved the problem. Has any one else had this problem and how did they fix it.

Heater core could be leaking.

I agree with Mike it sounds like the heater core.

It is not the heater core. It is the water that is collected from the trough under the grill on the front in front of the window. It is just water. Only get water in the car after a rain. Sorry about the description, I do not know the right terms for parts.

Oh I gotcha. I know where you are talking about. I think you might end up having to grind back that seam on the firewall. It should have a body putty inside it. You might have a leak though there. You could try laying on the silicone real heavy over the seam that might help. All those body seams in the firewall though are a real pain in the butt. try having someone pour water on it and see if you can find the source.

I know GTP's and such are infamous leakers. Our main problem is one that you are describing. To fix ours you need to remove that plastic piece at the bottom of the windshield. I believe it is the cover to the HVAC blower unit, you should be able to see on the weather stripping exactly where it is leaking because it will not be dirty/dusty but rather clean from water passing through.

everything from GM (the "fwd" age) leaked, from achieva's to sunfires, If you can get to the crack you can fix it at home, its not hard at all.