I had the same problem and was wondering where it was coming from. I figured out it was coming in through where the bolts that hold the spoiler on. I think there is 4 of them just open your trunk and look. I made sure they were all dry then i soaked the trunk down for a minute then feel the four bolts to see which one is wet and letting the water in. I just took the nut off one that was wet and put alot of silicone around the edge of the bolt and on the back of the nut (which has a washer attached to it) and tighten it back down, hasn't leaked in 6 months.
