After an initial trip in for diagnosis and a follow up visit for installation of parts & reprogramming (they gave me a loaner both times), I can't believe the difference. I keep looking to see if it's the same X!

Turns out I had a DSC Module with an internal short, which has now been replaced, and they also reprogrammed the DME under a sevice campaign - SIB 12 04 08.

Hats off to Tom Williams BMW, who took care of this for me under Goodwill even though I am the second owner and I am past the warranty period. (They had opened a PUMA case on these issues while in warranty after I bought the car from an individual who originally purchased the car there).

I am a happy man! Thanks, Weasel, for advice on how to approach!