it won't be original looking, exactly, but why not just cut the whole thing all new on a laser and do infill with ink that you like?
the secret that I use is to leave the paper masking on while lasering, etch the letters deeply by doing multiple passes or raising the laser bed a click between lettering passes, to dig deeper. leave the masking on, paint with acrylic paint, PUSH paint into voids, repeat until the paint fills the voids. let dry 1/2 hour or more. peel off backing paper, scrape off excess using soft burning tool (fingernail works great!) and you are done.
you can print mirror image on the underside if you want better protection and if you use clear plastic.
else, I use black, fill with white and it comes out nice and contrasty.
you could even have cut-outs for windows and press clear or red or other semi transparent plastic into that cut-out; to do that, you find what the laser kerf width is and add that to the 'lens' plastic when you cut it. try a few sizes until you can PRESS the lens into the plastic and it fits by force of friction.
repairing existing will never look good. just create a new one.