Update:
1) I did stop off at Darryl's and took him up on his kind offer to extinguish the light using his circuit board. Ahh! Nice to have a dark instrument cluster again. But OhNoes! After a week it's back on again.
I have a theory - based on the intermittent fault - it might be a bad clockspring. But I really don't know what I'm talking about. Anyone here know if there are any more likely failure modes compared to others? Would the "delayed reaction" indicate one fault as opposed to others? Same thing happened the last time I had it re-set: drove for a while, then it came back on.
2) As for mac being able to run Durametric: since on and Intel Mac you boot in a perfectly legit windows environment there's no reason why you can't run any windows software perfectly well. At least that's my experience.