When i did mine, i removed the axle completely away from the X and working on it. Yes i removed axle nut and replaced with new nut from dealer. I do not recommend you to replace the cv boot just "repack I with grease and pop A back in", it is not my way to treat her. Look at the picture you attached above, remove the axle nut and pull the axle completely out, hold (A) and using plastic heavy duty hammer band down the bearing case (I), install the new cv boot with grease and reassemble, you are done.

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BMW X5 2004 - 2005 MB E320
BMW 1999 528i/ 1998 Nissan PathFinder (sold)