Update as promised:
Well, it's not much of an update since I don't have any technical details to share. She's getting a new motor. They mentioned it was related to the rod bearings and left it at that. Mine is a very early build M3... and should now be getting the last of production M3 engines with all the learnings from the past 4 years baked in (?).
Won't have it back for a couple of weeks, and then need to do the break-in. On a another note, damn, my 335i loaner is nice. I used to have a 996 Turbo and I'm a sucker for gobs of torque. I'd like to try out a 335d sometime.
Also, thank God for CPO coverage...