my wife has a 2003 Olds Aurora that has a three piece roof and leaks at the driver side seam where it meets the windshield.
I found the leak to be at the roof seam where it meets the windshield, the seal had for some reason broken at that point and started leak through there. I scraped as mush as I could, there's only a quarter inch opening so you'll need a needle point tool to reach in and loosen as much dirt as possible and blow it out of the way and applied some (windshield and glass sealant) and that took care of the leak problem. Good luck, hope this is of some help to someone else.
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