Sorry you lost this one, but I suspect it had a yolk sac infection, which are almost impossible to treat. That crusty "thing" is the umbilicus, not the vent, and it looks infected to me. Only way to know for sure is to have a necropsy done at a lab. One can also try doing their own necropsy, though you might not see anything obvious.
Again, sorry for your loss.
thank you. I really appreciate all of the advice. I thought he was going to make it for a little while but then he just started getting weaker. I tried putting him in with the other babies but he just couldn't hang and kept getting mowed over so I stuck him back in the incubator and it just went downhill from there. I already disposed of him so I can't do a necropsy but I'm not sure I could anyways. I didn't even look at the three eggs that never hatched. Just too sad.