I have had mixed results with the permatex but never that bad, usually lasts between 1 to 5 years. I use a razor to make sure there is nothing left in the glass, never sand the metal backing piece, it needs to be flat and smooth, almost polished.
I use some acitone on the glass and metal part, then follow up with 100% achohol.
Then follow the directions, this is a situation where more is not better. The small drop is all that is needed.
I would do it on a relitively cool windshield.
