Ok. Daylight. Fresh Brain. Digested all the good advise. Start at the back and work forward. Right rear axle shaft has popped out. Why would this happen?



For reference the easiest way to pop it back in is to unload the axle by dumping the air in the system.
1. Jacked up right rear and secured an axle stand.
2. Using INPA dumped air from right rear and reservoir
3. Have a lovely assistance rotating the wheel slightly while prying against the chassis (did not like using the exhaust to pry).
4. Popped right in. Try a reverse pry to see if you can pop it back out easily or not.
5. Using INPA raise right rear.
6. Lowered car and tested.
7. Order new spring clip and seals to replace just to be sure.

So in hindsight...

1. As @andrewwynn suspected the key information is the grinding noise was when going from Neutral into Park. The pawl was likely unable to engage due to insufficient parasitic drag to slow the shaft down (what the shaft is called I am unsure).
2. First step should be to carry out a visual inspection in the day light starting at the wheels and working towards the transmission.
3. The parking pawl does not seem to lock the front driveshaft (a comment asked if the fuse was in or out, to confirm the fuse was only removed briefly).
4. There was rear suspension work carried out within the last 3 months. If you are having your commonly failed rear ball joints replaced (I had a whole kit done in the back end in Jan) make sure the mechanic checks the diff output shafts are engaged fully!
5. Check error codes. In my case it created error codes 51AD and 51AF in the transmission controller GS19A
6. The xoutpost community is awesome!
7. X5's are a love / hate relationship.

I will also edit the first post title message for future reference, hopefully to help someone else out.

I think we have dodged an expensive missile...

Thanks everyone for the help!
@SlickGT1
@andrewwynn
@wpoll