I recently purchased a 2003 E320 with only 42k miles. Car is in pristine condition except....every time I wash the car or the car is left in the rain the rear drive side floor board becomes soaking wet. That is the only part of the carpet that is wet. Not wet on the sides, front or other rear. I jacked up the car and took the dirt cover off then removed the plug directly underneath the floor pan and water poured out. Any ideas where the water would be coming from? Sunroof, rear window, or trunk?