J. B. Wood prodded the keyboard with:

Hello, all, especially those with familiarity with subject. I've
got a decades-old Stromberg-Carlson SC-2554 wall mount phone. It's
still in great shape except recently a small white piece of plastic
on the make/break hook switch broke rendering the rest of the cradle
mechanism inoperative. The plastic piece finally broke from the
tension from the return spring. It's a clean break but I'm afraid
that even if I can glue the pieces back together it will most likely
fail again in short order. Thanks for your time and your comment is
most appreciated.
Sincerely,

You could always try a steel pin heated hot enough to sink into the
plastic, a bit like a staple, or cross drill it and press a staple in
the holes.

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Best Regards:
Baron.