Excellent write-up! Great pictorial! I haven't noticed the dirt, but did notice the moisture around the third brake light in the late fall season that would accumulate around the edges when I washed the truck. I will definately use your advice to fix it.
Probably related, I notice a similiar dirt/water penetration around the edges of the headlights. I had purposed planned on waiting out the winter to see how they made out and then discuss this with the dealer at that point...basically wanted it to get worse to emphasize the issue. If I get a chance, I'll see if I can take some pics.