
I wouldn't worry about it too much. I'm still planning my repair on this prentiss so count your blessings its only "a little" broken lolAwesome restoration in the video. No concerns about the broken / missing casting on the body (non dynamic jaw side)?

I fixed it for you. One reason you see cracks is people use the slide as an anvil. But in the case of Prentiss, anecdotally it is much more common to find them with a slide crack in that exact location. I believe it is a weld line casting defect caused by bad mold design. Wikipedia explains is pretty well.We see a lot of old Prentiss vises with that same crack in the slide. Can anyone explain why that happens? It would seem that surface should not see any stress.
en.m.wikipedia.org