Was this ever solved?
 

im having the same problem right now, no one can replicate the leak. i saw bob farrs answer, but im hoping smokey found a solution, who was the original poster of the thread. HELP!

I'll throw this out incase it helps anyone else. The driver side sunroof drainage tube has a piece of plastic similar to this http://i44.tinypic.com/wssrpk.jpg that hooks up to the firewall. Then it drains the water down by where the bolt that holds the wiper motor is located. then all the way down to that little hole under the brake booster. that piece of plastic has a black rubber seal around it that dries up causing the water to leak back in. the parking brake assembly will get wet and so will the dead pedal+the foam under the carpet and bottom driver side floor board. You have to take out the entire dash for this job. apply some 100% weatherproof silicone sealant around the plastic and problem fixed.

.
This is actually not as big of a mystery as you would think. This is getting more and more common than you think. I think I know where your leak may be coming from. If you pop the driver side a/c vent out look closely all the way to the firewall where the sunroof drain hose hooks up. There is a white plastic style plug that snaps into firewall and this is the piece that the hose hooks to. Open sunroof all the way and have someone pour water in the drain while you observe the plug at the firewall and i believe you will be surprised at what you see. The water runs right back into the car past this cheesy black foam seal thats on it. I just maneuver them out of the firewall and coat them really good with seam sealer and reinstall them. Hope this helps guys

Wow I am having this exact same problem as well. Leaking water coming down my e brake pedal and pooling up. Pouring a few cups into my sunroof drain didn't produce the leak but maybe it wasn't enough to make it down. I do however see water coming out from the firewall area below the windshield wiper so i know some or most of the water is coming out. Sealed the grommet in that area as well because water was running over it and it was separating from the firewall a little. That did not fix the leak

The previous two posts have given me hope though. They both seem to be referring to the same thing but one says to remove the entire dash and the other says to remove the vent. I'll try to figure out the vent thing first

Hey I look at it like this, if the water is getting in, the leak can be found..

Yea. It's just frustrating when you can't reliably reproduce the leak. Ran hose over car for 5 minutes, poured water directly into sunroof drain, sprayed water directly into engine area where the water drains. None produced the leak.

Yea same thing over here. It would only showed up when it rain very heavy. It was such a relief when i found the culprit.

forgot to mention there's another grommet on the outside on the firewall that guides the engine fuse box cables. located behind and under the brake booster. Its pretty big you can't miss it. i had to put some duct tape around it because water was leaking in their as well. you can also see if its leaking by sticking your thumbs from the inside. its right on top the parking brake assembly if i remembered right. hope this helps!

do i need to take the entire dash apart to be able to stick my thumbs in it from the inside?
behind and under the brake booster pedal? im not following. is it the large grommet shown here on the right? thats the brake booster on the left

Attachment 193542

looking at the fsm. do i have to remove the entire dash to be able to pop the vent out as you describe?

No not at all. When you pop the lower dash panel off there may be a screw or something if I remember.

thanks. ill have to poke around. right now i have some tape covering the sunroof perimeter waiting for some rain so i can make sure thats where its getting in. Used blue painters tape and covered it with duct tape to make it less permeable - not sure if this is best

As long as it will work that is all that matters..hopefully you will get to the bottom of it.

Yes, that large grommet does leak. I had this leaking issue in 2012 and I put a silicone caulk around the grommet and it stopped.

I have small drips but I think mine is from condensation. Noticed a drip on the dead pedal a few times and thought I was losing my mind lol.