Of possible interest from my files --
REPAIR HARD RUBBER GRIPS
I have repaired a lot of old colt grips using clear epoxy glue, not the 5 minute kind. For a simple crack I put the glue on the inside and let it fill the crack, wiping off what comes thru to the outside. If the cracked piece is loose I clamp it. Otherwise I would just settle for having the crack filled and the piece stabilized.
For worse problems with Colt grips, like a piece missing, cracked away from a corner, etc.: I fix them by cleaning and roughing up the broken surface, wax a piece of foil and place it on the gun frame. Use plent of wax to avoid glue running away or sticking. Put the grips on, position them to avoid run-off, then fill the missing area with epoxy mixed with lamp black or carbon black. It may be necessary to do more than one application to get a good fill.
After it hardens, like overnight, you re-shape the area and polish it. An invisible repair is possible. If your job extends into the checkered area you are on your own, depending on your skill and artistry.
After notes: Do a couple dry runs on scrap the get the hang of it before you risk messing up a job. Epoxy glue is very tolerant of mixing in color so long as it is not water based. Artist colors, powder and liquid, oil paints and acrylic work OK. Any additive weakens the glue but strength is not much of a factor in grip repair and only a little of the black is needed.
Repair of New Service grip --