I'm planning on painting a previously painted (almost 80 y.o.)
basement
floor with oil-based floor/concrete paint.

Do you need to remove the existing paint before painting the floor? I
am just wondering whether the new paint will stick well with the
existing paint. If the paint manufacturer suggests removing the
existing paint, you will have a lot of hard work in front of you
because removing paint from concrete floor is a very difficult job (and
probably not very healthy); if this is the case, you may be better off
just leave the floor alone.

Jay Chan