fogged rear window?

Don't know what POs have done to the car. When f/r glass get removed from a car, it's possible to begin the process of delamination.

Usually delamination occurs around the edge of the glass. It is ALWAYS visible. If the fogging is not permanent, it's probably a seal issue as discussed. If it is permanent, it's delamination. Don't know if the average glass shop can relaminate a window. (I'm amazed at what they can do with stone chips.)