That is your rear gutter, it attaches to the rear of the sunroof carriage assembly. It also is what pushes your sunroof cover back when you open the sunroof. To put it back in place, you're going to have to take the glass out of the roof, and mount it on to the carriage again. I had to drill a hole in each side of mine, screw it in place, and silicone the screw heads. It has held up for the past 3 years with no problems. You definitely want to put this back in place again, as it diverts the water to the drain holes on either side. If not replaced, you're going to end up with a wet seat.
