Solved, see post 29.

Well, looks like I get to join what looks to be a rather frustrated club. Went outside after the X has been sitting for a week and the passenger front was lower than the lowest setting. Easily visibly noticeable. After a few seconds of hitting the unlock button on the FOB the truck aired up to proper height so it looks like a leak somewhere dealing with the right front.

I'm guessing that includes: right front airbag, front axle distribution valve/tank under the truck, and the fittings/lines associated with those. Will get a soapy water bottle ready when able to get it into the garage again. Been remodeling our master bath so I have the tub, vanity, and other accoutrements residing in Red's usual resting place.

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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)