To follow up on my original post, this problem turned out to be related to the instrument cluster replacement posts in this forum. Using information supplied here (can't remember your name, nor your post, but *thanks*, man, for the contact at BMW), I got in touch with BMW, who paid for the replacement part (over $500), while I paid for an hour's labor.
The lesson: I'll be researching any future issues before thinking of calling my local repair folks. On my original call to the repair guys, I got a vague kind of "never heard of this problem, could take a while to figure it out" (ka-CHING!). Lots easier to show up at the repair place with documentation and precedence for backing from BMW in hand.