Mine had to be replaced, not due to fogging, but to a BB (the upper rectangular glass piece). The Bago factory would not replace the one piece, only the whole unit. $818 in 2005. I had $250 ded, insurance picked up the rest.
I kept the old unit, thinking I could try & replace it myself for another day. First, it is very heavy. Second, the way it is all assembled with that black goo, hard to separate without breaking the other pieces, IMHO. After several hours I tossed it into the dumpster at the GNR.
Maybe a good glass shop could do it, but my guess is it would cost more than your deductable, unless yours is high. The rectangular window glass itself was $125.
Dan & Sharon & Kasey (Our Yorkie Puppy (11 Yrs Old) On the Road (2012 Journey 36M, 2006 Jeep Liberty)
USN-Ret ('65-'93) Fulltimers, Class of 2012