I was once told to cover a crack with a glue (don't remember what
kind) and lost the info when I changed computers. Since it worked
well before I would like to see if I can salvage this enough to
enjoy wearing it myself.
You could have a look at the Kingsley North website for glues that
fill imperfections on the surface of cabochons. These are intended to
be applied, cured, then the surface reground and repolished, so that
the filler remains only in the pit or crack.
The good products won’t yellow.