I just went through this on an '82 240D, during my first experience installing a set of rebuilt axles.
After stuggling for about an hour with assorted blunt tools to try and install those clips, I wound up using a 1/4" socket-driver handle (looks like a screwdriver) with a 1/4" drive extension, tipped by 6 or 7mm socket to stay put on those little nubs and push the clips home.

Happy Motoring, Mark

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DrDKW