Congrats on a fairly uncommon acquisition!
Certainly glad the basic casting units are still serviceable. You should be able to effect needed repairs fairly easily, while the visual demonstration value of the model seems mostly unaffected.
A 3D replacement flywheel sounds like a good short term solution, but meanwhile I'd definitely keep my eye out for a suitable metal replacement alternative.
I do really like those cutaway engines that serve to demonstrate the steam engines operations and functions!
Sooooooo .... your local post office keeps secrets from you too?!?!?