do you have reclining rear seats? i have to take a look at mine, to see if that's what the plastic trim on the sidewall of the trunk looks like, but this is what it reminds me of... option code S461A...

Just checked mine. Terminator is correct. That is a cover for the reclining mechanism on the side panel.

Ya I do have the electronic reclining seats. I will check tomorrow for anything that appears to be missing. I didn't notice anything being amiss. Thanks guys!

This is a side cover trim on your (vertical) seat back, which tells me your car has the electrically adjustable seat back angle.

Fold your two seat backs down, as if you were transporting something in the back. You'll see that one side has a plastic cover and the other (likely) does NOT. Then you know where to re-install it.

Take another look at the BMW part nbr on the back of the orig picture you posted and see if it reads: 52 20 7 012 909 ... if it does then it is item #2 in the diagram below and is for the LEFT rear seat.

BTW, was that the part number you where looking for on realoem.com? If yes, not sure why that number didn't come up in your search. :dunno:

Was the above part number & part correct? Just curious. :)

This is an interior trim piece.

As you know, the rear seats of your X5 have a reclining adjustment that allows the seats to recline as much as in one of those turboprop commuter planes. In other words, it is a worthless feature added to "me too" Mercedes.

The catch for the seat goes back and forth on a little electric motor controlled by a switch on the overhead console or in the rear of the car.

This piece you found is a bezel that covers the seat catch. There is one on each side, this appears to be the passenger side.

Yep! Mystery solved!

That piece was indeed missing. It just snapped right in there.

Qsilver7, yes that is the correct piece. I have no clue why it didn't show up on realoem. Guess I didn't really know what I was looking for :D

Great, glad it worked out and fit right back in. :thumbup: