I too recently found a C1 on FB, mine was a $200 "easy fix" but did come with a table. After tear down, I found the end assembly was broken. Any advice on how to fix it?
Yes, that is snow in the picture. The previous owner left it out in the cold to freeze to death..
That's actually fairly common damage caused by being dropped with the jaws at least partially open. The vise goes nose first into the ground and hits the spindle. The spindle pushes backwards on the nut and the pins break out the front of the tail cap assembly.
The best way I have found to fix them is to grind away the material that would normally be behind the pins (technically in front of the pins) and then TIG weld a large washer over that section (Inconel filler rod works best). I often have to change the washer OD and ID to match, but that's easy and it doesn't have to be perfect. I actually like the washer to be slightly smaller in outer diameter so there is a nice ridge I can use to weld along. If you just weld a washer in place without grinding down to the pin holes, the pins will move back and forth and they're supposed to be stationary.
After welding the washer in place I will reassemble the body of the vise with the nut and tail cap assembly, then put the whole thing is a very large vise using a length of round stock or a large socket to press the nut and tail cap assembly into position securely. If not, everything won't be lined up properly. I then re-drill the pin holes, normally going up a fraction...so from 1/4" to 5/16" or something similar. Remove it from the big vise, install the pins, smooth them with a flap disc and nobody will know the tail cap was ever damaged.
The first time I tried this I brazed the washer in place and it worked fine as well. The pins only come into play when you're opening the vise, so they don't see much of a load.
The first time I did this the tail cap assembly actually had very little material behind the pins, so I didn't have to remove much of anything before adding the washer. The pictures are the first time I tried it...flame cut the ID as you can see and then brazed it on the inside...not pretty, but it worked. Now I open the ID on the lathe and also make the OD smaller so I can weld on the outside...just a bit easier.



