I work on a client's 328xi. Very similar drive train to the e70.

He damaged his TC the oil leaked out and it burned up the clutch. We tried to just replace the oil no go. I had to replace the TC then everything back to normal.

The x-drive starts with the front disconnected and each time you start moving the TC variable clutch engages, I'm not a fan of the fact you can feel the front axle engage but once engaged it should not vibrate unless you have other drive train issues like the guibo being worn.

I have e53s and both are pre x-drive so they are full time 4wd no way to disconnect the front axle the TC is effectively open differential so you are dead in the water if a cv axle pops out of the dif but I prefer the simple TC solution to the far more complicated TC of the x-drive.

__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)