I finally got around to replacing the rear window. The delay came in having to special order the MB-Sealant - which I would not attempt to substitute with anything else.
I also finally had an opportunity to see how well the defroster works. Unfortunately there are about 8 bands right about in the middle of the window that don't work. They are separated by two good bands so after a short time the entire window clears!
In any event it is a far cry better than the POS I had in there before - massive delamination on both sides and only about 2 inches a working defroster on the very top.
It just looks soooooo much better.