E46Mango, it didn't break down, no. I'm presuming they haven't torn it apart and just had the cover off, frankly it hadn't felt like a problem before.
He's telling my $800 for a replacement used diff "through their distributors" and 5-6 hours to replace, though he'll "give me a break" and do 2 hrs... I've never dealt with anything behind the firewall before so I'm at a loss for experience, but I'm feeling like, until I start looking power or something, that I'm not really needing to have this repaired today. Frankly I'd been starting to look into planning mechanical upgrades, and I'd rather not buy a new used diff then want to upgrade it in a year again.
Unless, of course, I can get them to do it free under the warranty I'm beyond miles on now...