Thank you to all who offered advice.

I tried the teflon tape trick and it seems to be holding. It will be tried with primed shells first before progressing to low pressure 2 1/2 shells.

For want of a better term I used the word nipple. And it is a breech loading hammer 410.

Coming to think of it, maybe I could not find any parts because i used the wrong term when searching on the net!