I bought a very cheap non-working 414 on ebay and ripped it apart to see what makes it work. I also bought a repair manual.
The plastic piece that broke is part of the molded body - it's just a "pin" or rod. I could get another body and swap, but then I get into the Ship of Theseus paradox .

It is possible to drill a small hole and put in a small screw, but I could damage it further in the process. Some sort of epoxy could also cause issue or break again. For some reason, I want a reversible modification.

At the moment, I'm thinking of making an insert. It would fit over the base where the plastic piece was and extend upward. I think there is just enough room to do this. A small chunk of aluminum or hardened epoxy could be filed to slide in place.