It's the switch panel. I had to replace mine. The door bezel that holds the switches just pops out and then you just unscrew the switches from the underside of the bezel.
I'm glad you understood the question. I thought he was referring to "rear window" not the side windows at the rear. Unless he is referring to the defrost circuit in the "rear window" as being intermittent.
had the same issue, take out the 2 screws holding the driver's side switch panel to the actual rocker switches (under the drro handle/ door pull thing).. there are little copper connections that are made when you hit the window switches. I used a small pick and some wd-40 and cleaned all the contact points of the switches. Then tried my best to throw some dielectric grease in there to prolong any further corrosion/issues. All window switched work great now.
Initially, mine were so bad the rears didn't work at all and you had to fight with the fronts. I guess with water/dust/crap getting in the switches from the top being down makes them more prone to getting corroded