the sealant leak problems can be from the third brake light ( rrt #09-096 ) goop on silicone, no replacement gasket available. Better to make your own using the original gasket as a pattern, NAPA & other places sell gasket material in sheets, thicker & thinner, & in several types of materials
or the rear window, sometimes the sealant gets an air bubble & a small area is missed, sometimes the machine is bumped & misses a spot
the other area in the past that leaks is the vents between the cab & the bed, near the place where the upper & lower cab body is welded together
this guy had a similar problem & decided to fix it his own way'
Fixing the LEAKING rear window (3 steps)
I have spent a lot of time trying to figure out why my 07 QC with power window is wet in the back. Have made changes, run the hose over the top and back, removed rear seats, etc.. It turns out the truck was leaking in two places 1) The 3rd Brake light 2) The sliding window track. My solution is not something I have read on the forums, so I thought I would share.
First things first, you need to fix the third brake light. The weatherstripping they use breaks down in less than two years and will start to pass water. Remove the light, remove the weatherstripping, and put a nice bead of clear silicone caulk around the entire light. Reinstall.
If the third brake light is leaking, the water will enter in the middle, and trickle down one or both side of the curved ledge (above the window). When it reaches the back corner, it will trickle down, behind the plastic interior trim (where seatbelts are mounted), down to the floor, and make its way to the tool bins under the rear seats. To test if it is (still) leaking, stuff a piece of paper between the headliner and the rear ledge. Run the hose, and if water is entering from above, the paper will get wet.
The bigger problem is the leaking power rear window. Run the hose over the top of the truck (or just onto the sliding window) and inside the truck, you will see the sliding channel fill with water. If this is the case, there are two things you can do.
First is to narrow the channel. On my window, there was alot of play at the bottom of the window. As a result, the window was never pressed up against the rubber and it would quickly pass water. When the channel fills up, it spills over (usually) on one of the sides depending on how truck is parked.
Test to see if there is any play with the window. If there is, use a small hammer. Place a screwdriver on side of channel that you want to narrow. Carefully tap the back of the screwdriver until the channel is narrower. You only need to do this at the part of the channel that aligns with the edge of the window when it is closed. THe channel is metal underneath the plastic coating.
If you go too far, you can bend the channel out with the screwdriver.
Also, use rubber/vinyl protectant on these pieces. Mine have started to dry out and I want them to last as long as possible.
I have run the hose over the back and no longer see any water leaking into the channel. However, the last thing I did was to install small drains under the rear channel.
Find a small straw (coffee swizzle), and drill two holes, one at each end of the channel. If you drill at an angle, it will drill though the cauk between the window and behind the channel. Cut small pieces of the straw for a drain. Coat the outside of the straw with sealant and push it down into the holes you have drilled. Now, if any water does make its way into the channel, it will drain out underneath the rear window. The holes you drill need to be exactly the same size as the straw you use. Also you need to use sealant around the straw or the water will drain into the truck. THe drains will flow small amounts of water, if there is a major leak around the rear window, they will not be able to keep up.
1) Fix rear brake light
2) Narrow sliding channel so there is no play, and window is held fast against the rubber.
3) Install small drains in bottom of channel.