The black plastic frame -- closest to the rear window - cracked at the hole holding the small rubber bumper. Most likely it was hit when one of the guys at the car wash cleaned the rear window.

It looks like the frame is glued to the window - is this correct? It would be easier to remove it from the car to glue it up.

 

Definitely not supposed to be glued to the window, lol... Your car's previous owner hacked it...

 

It should have two metal brackets glued to the glass (just like a rearview mirror) and the brake plastic housing clips into the brackets. If the brackets came unglued, just use rearview mirror glue to reattach them.

 

Thanks -- I will take another look at it. No previous owner - I will try and remove.

 

Just took mine apart for cleaning, you need small hands for this-
1. pull off outer shell - depress two tabs underneath it that poke through square holes and then pull straight back (towards the front of the car)
2. depress tabs on each side of the rectangular light fixture and pull straight back GENTLY, the two power wires REMAIN ATTACHED but have enough slack to rest it down on the rear deck
3. slide the black-plastic bracket upwards, along the plane of the rear window AFTER releasing by pulling-forward slightly the two tabs that lock it in place, these tabs are underneath it, just above the rear deck - you need tiny fingers with quite a bit of strength, I used my pinky... You might be able to do it with a screwdriver, but it would be hard to access with a straight tool. The bracket has the wires running through a hole, so again, it will be captive to the car unless you disconnect the wires (no idea how as they appear soldered and I only needed to clean mine, not replace it)