Radiator Cap Repair

[spinelll]

I flipped open my radiator cap and it separated from the hinged part of the base. This cap does not have a temp gauge.
A few guys said that the bolt was missing but there was never a bolt in there.
The area marked "A" is actually recessed.
I can push "A" into "B" and it will lock to the main base when you twist it but I'd prefer to secure it to that piece with the hinge.

Is there a way to repair this?

Thanks
Leo