Shear Pins

Kern Dog said

I'm only guessing but I suspect that they injected hot plastic into specific channels that hardened as it cooled down

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I agree that is how they are made.

As for the need...

As long as the rest of the plastic is intact and the shafts are the correct length there should be no issues.

If the plastic "pins" are missing you could get some epoxy and a large syringe and inject it into the holes.

That should lock it in place.