You can loosen the inner fender lining to get at it... but it's not fun. Wheel arch rivets need to be drilled out and lots of 8mm screws and pushpins.

Alternatively you could use a borescope (I own one for plumbing issues) to see if you can get a bead on it to have a general idea where to use your grabber tool. Borescopes are very handy to have around the house anyway, and cheap on Amazon.

Beyond those two options... just keep at it and hope to get lucky.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)