I am not sure if it was on the forum or not but within the last 2 months someone posted info on a kit you could buy to restore your defroster/defogger.
You can buy a kit or buy the individual grid lines and the heavier sides.

I have and have used some of the Permatex Grid Repair Liquid but on my window the corrosion was too wide spread and I also found I could not easily paint on a whole grid with the slanting of the window and the room available.
When I had the Window out it could have been done.
If you want to see what it looks like there is a picture on Amazon as the sell it their.
The Autozone type place counter guys did not know what it was but 2 of the privatly owned Autopart stores had it. It can be anywere from $8-$13 per littl vile.
I have used it with success on scratched grids in the past.

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84 300D, 82 Volvo 244Gl Diesel