Update to my stupidity:
I contacted the RDZ company via a web contact form and explained how I had broken their well constructed tool. The company advised me about their replacement inner core and I now understand that the holding hex screw can sometimes be a little tight to move.
They will sell me a new inner and are adding a replacement core gratis. They have also offered to find the cheapest shipping option too. Incredibly helpful, kindness beyond necessity and great customer service. So here is my shout out to RDZ…
If MC Etcher is out of stock, give these people a try (if you are in the USA) because they went the extra 10 miles for me. Thank you for the suggestion to explore the warranty, @gdon_2003. It was an excellent suggestion, Guy.