Originally Posted by Qsilver7

Ditto the replies above. You have item #4 (the cassette box) in the diagram below. There's also a #4 (CD box) which has a different 11 digit part number.

What you want is #1...and you probably can find them in 99% of e53 X5s you can find in junk yards all over the country....and you can copy and paste the correct 11 digit BMW part number for #1 in an ebay or amazon.com or google search box to see if you can find used ones (and possibly newer ones) for less. Fortunately white46 gave you a direct link to the part number database which makes it easy for you to get the correct 11 digit BMW part number for #1.

It's a slide-out...slide-in replacement if you want to undertake the swap: