5th gen 4Runners suffer from a vortex of dust, which sucks it all up under the rear hatch as well as coating the window. When washing your 4runner after a trip, make sure you plug the drain holes at the base of the tailgate window, or all that dust will be washed down within the tailgate, eventually plugging it.
And the dealer will ask how often you submerge your truck in deep water, lol. Then, when your tailgate window stops working, they'll tell you it's because you operated your vehicle in a manner for which it was not intended.
Thanks for nothing, Roseville Toyota.