Need more tips for rear water leak

I have the common water leak that leaves the carpet wet in the left rear corner of my 2003 extended cab every time it rains. I've tried every recommendation I could find on this forum, but I haven't suceeded in fixing the problem. So far, I've done the following:

- cleaned the sliding window channel to make sure there was no buildup and drainage holes in the window seal were clean (although I could not really identify where they drain out)
- reamed the inside channel of the window trim to make sure water flows freely from the top of the cab (where the top cab trim tucks into the window trim) to the weep hole at the bottom of the window trim. Water flows freely out the weeper.
- replaced the third brake light lens gasket
- caulked the third brake light housing-to-cab interface. I had to caulk this because the housing would not come off the cab. Something was holding it from the inside, or the original gasket was really cemented in place. So I gently pulled it back about 3/8" and carefully caulked the seam just to make sure it isn't leaking.
- caulked a little plastic pin that helps hold the upper cab gasket to the cab (not the gasket on the door). I was sure this was the problem because that pin penetrates the cab housing, and I could see water running down the inside of window (inside the cab) when I poured water in that gap between the closed back door and the cab.

After all this - it still leaks. Does anyone have any other ideas? Are there any other drain holes that I missed, especially at the top of the cab? The tail end of that top cab/door gasket was glued in place, so I did not want to pull that back, but is there something else up in that area that could be leaking (like a weep hole or drainage channel), that I missed?

My only next option is to remove the headliner and inside trim to pinpoint exactly where the water is weeping in, but I really don't want to pull all that apart. I'm almost certain to damage the headliner attempting to remove it..

Any help is greatly appreciated. Thanks!

 

Some people have also found that tears in the bulbous door seal will cause water to make its way inside also. PHM saw this with a tear on the seal along his A-pillar, IIRC.

Have you pinpointed the condition that causes it? Like, does it only happen if you're driving in the rain? Does it happen when you park on the street or an incline where the driver's side is higher? Or only when the nose is higher, or the rear is higher? If you don't park on level ground, water can sometimes work its way into stuff.

A water hose (active test), and clear packing tape (passive test) are your friends here. It will help a lot if you remove anything that obstructs your inside of the water origin, which may also mean removing your rear seat on that side of the truck.

Passive way to test with tape is simple - For example, one-by-one, tape things off. Maybe start by completely covering the 3rd brake light with one piece of clear tape, taping from edge of roof to edge of roof so there's no possible way water could enter. Then repeat whatever condition causes it and see if the leak continues. If it still leaks, consider taping the entire roof rail channels from windshield to rear window, so water can't possibly enter the channel. If it continues to leak, consider taping from the top corner of the rear passenger door down to the base of its window (see what I'm saying in pic below). If it still leaks, tape around the entire rear window perimeter. If it still leaks, consider taping a sheet over the rear window. Yes, I know that'll look ugly, but it'll rule that out as a suspect.

Active way to test would be gutting that side of the interior and, starting from the bottom up, hit the potential spots you think it could be happening. Like, pull the rear out, have someone take a sprayer and spray along the bottom of the rear window, back and forth, and wait to see if there's water entry inside. If not, move up some, spraying left-to-right, until you see water. If none by the time you get to the the roof-channel-to-window-frame seal, then do the 3rd brake light. If none there holding the hose on it, head over to the door and spray it down.

I've heard of people dusting interior walls with baby powder and looking for leak lines. I think it's overkill.

I noticed my rear window was the source, because I could clearly see a drip line on the glass when shining a flashlight across the window at dark. Any chance you see water across your glass? This is what mine looked like. Notice the void in the drip where I smeared my finger across the drip.