Had to disassemble cap, cut apart cap rings, rebuild entire cap innards and barrel front end.
Bored out part of the original plastic inner barrel to replace with brass.
Montblanc forms the cap rings as one piece and the cap is injection molded around the rings, leaving only part of the ring unit exposed.
Final brass innards, original black plastic cap, rings cut apart, new black rings to fit between the metal rings.
Testing the fit.
Gluing things together.