Your Leer dealer might carry the rubber seal for the tailgate. Goes on the bed not the tailgate. It works good across the bottom and most of the way up the sides on my 2011. I needed to stop the water where the rear door bottom seal, adjustment to the door ltches, and the center brake light was leaking. I built up the bottom of the window/door gutter in the corners where the flat rubber pieces are riveted to the cap. Sealed the top of the rubber and forced the water run off in toward the center edge of the gutter channel instead of the outside edge where it would run into the gap of the tailgate.
