I just noticed my Malibu has the same leak ive seen ppl post on here. I have called GM and apparently not enough ppl have complained to trigger a recall. 4 years and I would have never noticed as I never sit in the back, but today as its pouring rain one of my friends noticed it. My roof interior and rear seat passenger have endured damage for who knows how long. Ive seen many posts on here with the same thing, its clearly factory/manufacturer responsibilty. Please call GM and complain and make sure to ask for your case number. I called and it took me less than 10 mins. They need to repair the issue and replace the upholstery that most likely now has mold. 800-222-1020