I just go to O'reilly's or Auto Zone or Advanced Auto parts, tell them your car info, and tell them you want Bosch OE direct replacement. They will order the part if not in stock. I did this for both pre and post. I did buy PB Blaster (spray can like WD40) penetrates the area to loosen it. After driving home, let the car sit to cool off then spray generously, repeat for 2 consecutive days. Then took a open ended 17mm wrench I believe and it came off easy breezy. No special tools. No swearing, mine is 4.4i 2003.

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2003 BMW E53 X5 4.4i - M62 engine (Non Sport with Premium and Cold Weather Package)
Color: Steel Gray Metallic
Mods:4.6is Exhaust (Pipes, Mufflers and chrome oval tips) BMW Sport package Taillamps, BMW Tire Valve Stem Caps
Medium tinted front windows
JVC HD Radio
Alpine 4x100 channel Amp
Orion 600W Mono HC Amp
Three 12" Sony Xplode in subwoofer enclosure