Can confirm. It happens. Usually in a car driven mostly without passengers. Passenger side valve will fall but go unnoticed by driver until that side fails.

My failure was both sides. But mine failed open so even when ac was on hot air would emanate from the center console area. That's on an e36 with dual climate though, not e53.

Andrew is right though. Further diagnosis could confirm the failure before actual removal. At certain mileages though I like to shotgun parts to establish a baseline for systems. Alpine, you didn't say your mileage (or I missed it) but I'm guessing the valve is due for replacement

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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)