Thanks for all the advice guys. Just checking in again now. No progress since yesterday - I'm working on other things. I think I know enough from all this discussion now. It does not make sense for me to buy a $200+ pressure tester tool at this point, but I'll see how things play out.

The X5 is at home, in the driveway, I assume.

Regarding cn90's wise note about not risking a major problem ... the only urgency is that my 17-year-old daughter wants to drive the X5 to school, etc. rather than my old Lexus, until I get back home in 2-3 more weeks. So nobody is really stranded and nothing bad will happen. I am hoping that we'll have a good learning experience if she is motivated enough to work with me over the phone to check, isolate, and fix things herself. We'll see on that one too. But I'll make sure nothing bad happens.

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2001 X5 3.0i, 203k miles, AT, owned since 2014