Maybe too late but I have 4.0 differential parts to sell
I blew the right cover off my 2006 650 (with 4.0 gears) 3 weeks ago, the fluid was contaminated, and I didn't want to mess with trying to put it all together (too many thumbs).
So I bought the whole differential. OUCH
Had 1250 miles on it when it blew.
I did not take it apart so I don' t know what shape the insides are.
It looks good from what you can see and there were no shavings or pieces. It all turns OK. Attached is a photo showing how the case broke. Its the whole thing including the actuator.
Let me know if still interested.