Just a shot in the dark, when old window tint is removed sometimes they are impatient and will use a razor and destroy the traces instead of steaming it off and scrubbing off the glue. If a trace gets cut anywhere that defroster line wont work. I don't know your particular situation however. Just visualy check the traces on the inside of the window from the connectors for small breaks.As far as prolonging the rear window fall out problem listed above, I noticed that when I drove with the top up and the windows down the rear glass would vibrate like crazy in the rearview mirror. When I rolled up the windows it stopped. Maybe keeping the windows closed could delay this problem, or maybe not. Just a thought.