Its much easier with the diff out of the car, but removing and installing it can be a pain too. Its good to have a buddy help you. I did it this past weekend with the diff out. The seals need to be pulled with some force with a crow bar or some type of strong hook. carefull not to gouge anything.
the new seals need to be banged in straight or pressed in. you can use the old seal and place it on top of the new seal to make sure you have an even contact surface to wack it in.
the shafts just pry out with a crow bar. You may want to replace the lock rings for the output shafts. they can also be a pita if the diff isn't out. I'm speaking from experience from a 535i, yours may be different.
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