I have not done any investigation yet, just wanted to see if anybody has seen this before and maybe has any idea if it is a quick fix.

I bought a 2007 GT Convertible in January. in Buffalo.... I finally got it out and drove it Columbus Ohio last week. everything went ok until I drove it through the car wash before going home. it leaked a little around the drivers door window, but nothing crazy. the real surprise happened when I pulled out of the bay and it looked like somebody was pouring a gallon jug of water out of the air box.

I had the A/C on. not sure if it somehow came in through a cabin air flter or if there is a drain that is plugged.

 

Open up the hood and look into the cowl area on the bottom. There are rubber drain tubes that get plugged up, and more than likely that is your problem. Good time to check the air intake filter while you are in there.

 

Sounds like your wiper cowl drains are plugged. you can find the little rubber nipples along the bottom of the firewall in the engine bay. Also the wiper cowl clips have a tendency to leak, because they have a foam seal under them.

 

Search 'water leak' and see the TSBs associated with it....
https://mustangforums.com/forum/search.php