Rear wiper arm cover question.

[Estroil 4.8is]

My 2000 X5 has always been missing the cover for the rear wiper arm bolt. So I ordered the part from Morristown BMW using the Part number from Realoem.com. I got it in the mail today and the cover does not fit. It's way to small to fit over my existing arm. So I'm wondering if I have the wrong arm on the X. It looks like there is just a button cover to hide the bolt. There is a small notch that looks like its there to get a small screwdriver under to remove the cover to get to the bolt. Here is the pic I looked at. My arm looks totally different. Part #3 is metal on my truck and its part of the arm not just a cover. Also there is a hole in #3 thats were the bolt is showing. I need a cover for that. I wish I had my camera It would be easier to show.