Nate,
Pretty old knives! Unfortunately the shop cannot "tighten" this up as rust and epoxy have formed and hardened, according to Scott, making it impossible to try and "move" that wooden handle.
That's the bad news. The "good" news is that the shop can fill it. It's a matter of mixing a little black dust of micarta with epoxy and filling the crack. You may notice the slight color variation...or not..."but"...(My favorite interjection)...it'll be
gap-free"!
Hope this helps, Capt. Chris