Going thru the process of doing the Rattle Trap sound proofing and noticed that there was a puddle of clean water that had soaked the rear carpet and there was some pooling in the LR foot well. It looks like a recent event since there is no evidence of rust, mold, mildew or nasty smell. The wet part goes as far forward as the driver's seatbelt attachment to the floor, right at the B-pillar. I also noticed some discoloration on the lower part of the seatbelt. I checked the door seals and they look fine. I did adjust the door latches a little snugger last week to clear up some wind noise. Anyway, is there a more likely place to look than another? I did go thru one puddle about 8" deep at 30MPH. No, not on purpose!

 

Rear window, maybe?

 

Some of these trucks have a known rear window leak problem.

 

3rd brake light

 

As said, check both the 3rd brake light and the rear window. My 06 and my buddies 06 both were leaking along the top of the rear window. A tube of window sealer from the local AutoZone fixed em both.

 

Well, it's not the 3rd brakelight or the running lights! The wet area is right along the carpet edge from the driver's seat belt attaching point to the front of the rear footwell. No signs of infiltration but there are streaks along the lower door gasket as well as the marks on the seatbelt (mentioned above). I'm going to have to chalk the gasket and see if I can find the entry point. So far the rear panel and rear seats are out. If it's over 50 tomorrow I'll Rattle Trap the back wall along with "Right Stuffing" the voids between panels. That stuff is GREAT!

 

I don't suppose one of the rear exhaust vents on the back of the cab is missing or upside down?

 

Nope! Checked them both.

 

I will assure that your issue is the rear window leaking. I had the same thing happen numerous times since new and finally changed that crap sliding rear window for a single pane (no slider)and all of my problems gone. I kick myself in the butt for not doing it sooner, before it claimed a 300.00 pair of binoculars

 

I had the same problem it sounds like but my leak was from the satellite radio antenna. It was loose and allowing water to leak in and run across the headliner and down the pillar. Once I caulked up that hole, it's been dry ever since. Might be worth checking if you have that antenna.

 

I think you were correct! Even though mine is an '06, I used some clear silicone on the rear window and the gap in the upper front door seal. Once I pushed the seal back I could see the gap between the pieces. Haven't had a good rain to test the mods, but I think it is fixed.

 

I have sealed the third brake light and run all the way around the back window with silicone and still have a leak. The compartment under the back seat will fill with water in a good rain. Been fighting it for a year now and im about ready to break it so insurance will buy a new glass to seeif that will fix it.