If he still has a 1900, 1901, 1902 catalog... its very likely the catalog is actually worth more than the gun!!!! Seriously!
I would scrub that barrel out as well as you can and give it a shot, it probably is not going to shoot MOA but it might still have life in it.
The 23D is a desirable gun as well. I personally don't chase them around but mostly b/c I am a lefty but I know the guys say the D can be a harder model to find. Sounds like GGndpa has good taste.
Congrats
