Well we have been getting some constant rain the past few days and hopped in the truck to go to the gas station and when backing out of my driveway noticed a few water drops on the top of the rear seat. I went to the store and on my way back tried to watch the best I can and noticed a constant drip while driving in the rain. And it turns into a water fall when I make left hand turns so im thinking that the 3rd brake light seal may be allowing it to leak in. I dont think its the cab de-pressurization strip on top of the cab since its only left turns that cause the waterfall. Any insite?

 

I have some insight...I just got done fixing a bunch of leaks in the back of my truck, and I actually still have the interior torn apart and the headliner out of it (gonna have the dent wizard fix a ding or two on the roof while it's a apart.

Yes, the third brake light may be leaking, and the gasket is only available with the complete lens. I band aided mine with a little rtv style sealer and so far so good. My rear window was also leaking, but I have a rear slider that has been replaced 3 times under warranty, and the last time they did a crappy job. If your rear window seal is factory, I'm going to guess that it's not leaking.

Now on my truck, which is a rcsb, I found a body seam on both sides of the roof behind the driver's door, that goes under that drip rail weatherstrip, and the factory bondo was all cracked on those seams, so I also resealed those.

After I got all of the higer leaks fixed, I found my body vents leaking, and the weatherstrip sealer didn't work on them, so I replaced them, and wouldn't ya know it, the new ones have been redesigned (and were only $7.50 each my cost, but it took me hours to remove the sealer that I tried on the originals )

First things that I'd look at would be the third brake light and those body seams...

 

like bud said, check your third brakelight. my old one was cracked and channeled water down to the rocker and rusted a hole in it so definately take care of it early.

 

i never thought to check the 3rd brake light. i have a sliding rear window. it leaks. have some nice rust going on. aggravates the **** out of me.

 

I feel your pain brother

I think that I have mine squared away now as far as water entering the cabin, but there's still some ugly rust going on...gonna clean it up with something like POR maybe.

I can't believe that I didn't take any pics of my whole water leak fiasco, I'm usually a big pic *****...but, I've been real busy lately though and didn't have the time to even find where I left the camera

 

The sliding windows have a hard black trim around them that would crack and cause leaks. Would have to be replaced.

 

Yessir, the dealer put 3 factory plastic framed rear sliders on mine, and everyone cracked on both sides of the upper corners. Water would literally pour in when it rained. Finally they got the OK to install an aftermarket CR Lawrence rear window and the window itself has been great. Shitty installation though...seems like they used a different company to seal the last one, as the first 2 replacements had nice clean installs, while the last looked sloppy, and eventually started leaking through the sealer I sealed it up myself and so far so good (fingers crossed)

 

I have the same problem with my a leak in the back...but I cant actaully see mine! I just replaced the third brake light with a L.E.D light with a new gasket. However it was leaking before that but I thought it was the gasket and it would not leak anymore but here we are...still leaking! All I know is after a good rain the rear passenger seatbelt is soaked and its leaking behind that pillar panel. I have been meaning to hit it up with a water hose but not time...need to make some before its to late though...Ya think its the rear window or the gasket still?

 

Best way to tell is to water test it like you mentioned, could be either or those, or even a body seam on the roof...

 

I like to turn on the air full blast, and spray soapy water on the outside. It should bubble up where the leak is coming from.