An update.
I followed Colin g's advice, and completed the fracture, so to speak. It was very easy to do; the crack was even worse than I thought.
Then I roughened the surfaces, for the glue to work better.
After degreasing, I applied the JB Weld 50139 Plastic Bonder.
Not a good photo, but on here I wanted to show that I enlarged the tp, with the intention to use a metal tp insert (a piece of a 4 mm metal tube), and secure that in place with epoxy putty.
I thought that might give this weak spot some more strength, than only glueing it together?
Any ideas on this?
I expect my repair to be unsuccesful.
But who knows.
Looks like the crack has spread. Another thing that destroys plastic over time is oil depending on plastic and UV light.
I hope it works out.. I think it has a fighting chance at least, and you certainly have nothing to lose...
Personally, I'd make something up in metal... brass would be nice
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.