Walter R. wrote:
If you have a buddy who has welding equipment, ask him to weld it.
Cast iron can be welded.

My sewer stack has a hairline crack in the bell hub right at the
concrete floor in my basement. I'm afraid the only way to fix it is
to bust out the floor around it and replace it, But I was hoping
for some suggestions for an epoxy or resin, or something that I
could do to fix the seeping crack. I'm wondering if I could build
up some mortar or something around it to try to seal the leak. It
is about an inch above the floor. Anyone have any ideas?

While cast iron can be welded, it is difficult. Brazing is simpler, however,
the OP mentioned that
the problem is at the bell hub. Welding it will melt the lead seal and
destroy the oakum caulk under
the lead. Getting it resealed may be difficult if not nearly impossible as
these materials are not used
now.