Stan, what kind of glue was used for that behind the tang repair?
That's kind of why I did my experiment to find out which adhesive would give me the most undetectable glue joint. Of course, that's only half the battle. You also need a perfectly fitted piece of wood that matches as closely as possible, and then you need to clamp correctly and control glue squeeze out as much as possible, cleaning most of it as you clamp and before the glue sets.
That was a big problem I saw with the polyurethane glue. Unless it would be possible to sand deep enough to remove the glue stain, it acted like a sealer and the joint was very visible under stock finish.
At this point, your options would likely be hiding the joint with a faux grain, which is ridiculously expensive unless you can learn to do it yourself. Or you could patch over the patch with another thin veneer of matching walnut that extended just beyond the current repair. But even with a perfect grain match, you still have a cross grain section at the rear that is harder to conceal under the best of circumstances. Of course, the perfect place to hide that part of the glue joint would be about an inch further back in the vee of checkering border.
