I gave up trying to squeeze in under the X5, sitting precariously on one jackstand, resting on a broken board on sand/gravel. I dug out my "truck" ramps that had been under my trailer in the garage, and drove the X5 up onto them. Much better, feel safer underneath.

While under there, I looked around at all the "new to me parts", and was pleased to see no sign of leaks (some seepage, though, on the oil pan), no loose or missing parts, and driveshafts, guibos, and rubber boots were good. My friend that was fixing it up for me over the previous 3.5 years before we swapped cars, did a good job. I haven't found the source of my codes, but they started months after I got the X5 from him.

I did re-route the mystery tube to near the bracket that had an empty clip; that must be where it had been, so I just zip-tied it to the dipstick, instead, because my fingers weren't nimble enough to use that clip. Fair enough.
here's the empty tube clip

I put the truck back on the ground, and tomorrow I'll start afresh, looking for the source of the vacuum leak. I found out how to remove the micro filter housing, etc. from over the engine (I added an addendum to my previous post about two videos that clued me in). Smoke tester first, carb cleaner second (while the engine is idling, while monitoring the Torque Pro app on my phone), and hope for the best.
Added 3/26: homemade smoke tester failed after warm-up, the $7 soldering iron burnt-out after only 30 minutes of total usage...my advice, don't build one like mine!

__________________
01 BMW X5 E53,3.0i-5L40E, 7/13/01
topas-blau,Leder-grau,"resto-project car"

Here:
14 Lexus ES350,3.5L-U660E
09 HHR Panel,2.2L-4T45E
04 Chevy 2500HD,6.0L-4L80E
98 GMC Sierra 1500,5.7L-4L60E

Gone:
66 Chevelle Malibu 2dr ht.,327>441c.i.-TH350>PGlide/transbrake
08 Cobalt Coupe,2.2L-4T45E
69 & 75 C10s,350c.i.-TH350
86 S10,2.8L-700R4
73 Volvo 142,2.0L-MT4
72 & 73 VW SuperBeetles,1.6l-MT4
64 VW,1.2l-MT4
67 Dodge Monaco 500 2dr ht.,383c.i.-A727
56 Chevy 210 4dr,265c.i.-PGlide