What should I do about the hour marker lume on my Titan?

A bit hard to see in the attached picture but the lume is still there in the 5 o'clock marker but it is gone from the 4 O'clock marker. It came out as a single piece. I am not sure if it was originally painted in or if it was a cast piece that was glued in.

Should I just paint in lume or should I be trying to carve a little piece of glowing plastic of some sort to glue in? I have several missing but I only found one.
Thanks for any advice,
John