Thanks for your answers.
I don't know if the windshield has been replaced recently, I just bought it a couple of months ago. Everything else seems to be in really good condition so this was the last thing I thought could fail.
The most annoying thing in this story is that when this part fell off, it also scratched and dented the side of the car. My Z was 100% free from dents and scratches before this happened... Aaargh!
Yep I will visit my local Nissan dealership on Monday to see what the can do for me. I just hope this will open your eyes to make sure it doesn't happen to you
Again, thanks.