Well, I finally decided to tackle the pesky water leak. I pulled the Expedition into the garage and tested the seals around the 3rd row seat windows and didn't find a leak. So, figured it had to be coming from the roof rack bolt holes or the cracks in the roof channel (see pics of cracks in first post in this thread). So I purchased some Permatex flowable clear silicone windshield & glass sealer. I setup my lightweight foldable work platform. I worked one side and then the other to pull off the roof rack by removing the 7 mounting screws on left and right side rails (T25 bit). Vacuumed all the dirt and grime from under the roof rack rails and the recessed screw holes. Took the roof rack outside and cleaned it up with some soapy water and a scrub brush. Then rinsed it off and left it out to dry.
I went back to the Expedition and cleaned the recessed roof channel on the drivers and passenger side to remove dirt and dust. I opened the Permatex flowable silicon package, cut the tip of the dispensing nozzle to be pretty small and screwed it onto the tube. With nitrile gloves on, I slowly squeezed the silicone into the cracks all down the sides of the roof channel. I was careful not to apply too much. It did as advertised "Wicking action silicone “seeks the leak”. Flows into hidden and hard-to-reach areas. Forms a tough, waterproof, durable, clear seal that is resistant to weather, extreme temperatures, vibration, shock and most shop chemicals. Fills surface voids and irregularities." Then ran a gloved finger down the length of the roof channel to further press the excess into the cracks. Used a shop towel with light pressure to clean up any visible excess silicone. The consistency of this silicon product is much thinner than any silicone product I've ever used and really does flow well into the gaps.
Then took the 14 roof rack screws and wound Teflon thread seal tape around each. Went back to the roof and squeezed a dab of the silicone into each of the 14 screw holes in the roof. Set the roof rack back in place on the roof. Reinserted each of the screws and gave them a few turns. Came back and tightened each until they were seated and tight.
I pulled the Expedition out of the garage today so I could inspect it in the sun. I was pleased how well the clear silicone filled the gaps and moreover how clean and undetectable it was. Products specs say that it takes 24-hours to fully cure. I'll probably give it an extra day or so and then run it through the drive-though car wash for a test. I'll report back on what I find.
