Car was fixed by BMW at no cost to me and is back in the garage tonight.
To help or give some information to those facing a similar issue, here's what I did:
- I put together a binder of information; made a printout of the differential bolt issue thread on this site and highlighted important parts. Made printouts of the "damage" and the broken bolt. After arguing with all of you here I worked to consolidate and perfect my "60 second pitch" outlining why I was convinced this was a warranty issue, e.g. force necessary to shear that bolt would have shattered the cover.
- Took two weeks to get my ducks in a row; briefed my lawyer; put together basically a ten step plan with continuing higher levels of escalation. Got some analysis done by a friend who works as an expert witness for structural failures in industry; he was able to give me some good basic comparative data.
First step was calling BMW NA. They basically told me to go fuck myself. They put an "complaint specialist" on the phone who I guess is extra good at telling people where to go. Amusing but expected.
Second step was meeting with the service manager of my local dealership. I presented my case to him and stressed I wanted to keep the good relationship I have with the dealership intact. I told him I understood the issue was with BMW NA but I wanted to feel like he and the dealership were on my side. I was able to get him to say that he agreed with me in my analysis of the issue.
A week later he called me and told me BMW would be covering everything 100%. Week later car is home. I am very appreciative of the service manager for helping me out in this case.
My takeaway? Dealing with BMW NA without a lawyer is pointless. You need your dealership on your side or be ready to go to court. People at your dealership have personal relationships with folks at BMW NA corporate that we/you/I just don't have.