That's the X3/X5 version with the plastic gear and part that you linked. Didn't know that was available from BMW actually.
There is no plastic gear in the e90/e60 transfer case actuator. The worm gear in the next to last picture is usually the one that wears down in our cars, is made of metal, and is available to be replaced by aftermarket parts (vanos-bmw.com, ebay). There is no OE/OEM part sold separately though.
Yours looks to be in decent shape, so I don't think that's your problem.
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