I was puting on the rear splash guards and this vented thing fell off . It was loose behind the passenger side wheel well on the rear. When I cut the plastic heads off the rivets to slip on the metal clips, this part fell on the ground . There is no corresponding part on the other side, the existing slots in the well are identical on both sides, there is no place to put this thing. It has movable rubber flaps on it as if to vent something. There are retaining clips built in and the top is labelled "Top". Can someone look under the rear portion of passenger side outside the wheel well, underneath in the muffler region and let me hnow what you find. 300C model. I will check with the dealer tomorrow but no C in stock to look at.