I just received one of my recent purchaces, I think it's a fairly late Mabie Todd Swan. It's a nice looking pen, simple black plastic with gold trim. It's a modern type plastic, I'm guessing something in the direction of polyester or pvc, it's hard and shiny, but not like celluloid or acetate.

Inside is a broken metal bit, part that pushes the sack flat. I'm not sure how it works in a leverless model, there is a screw device on top. I need to track down the right size rubber sack and metal bit, and figure out how the mechanical part work.