There is no magic here. It is a bit of a crap shoot. Generally you pay
more for new, and you get more, but sometimes rebuilt outlasts new.
Vacuum powered instruments are notoriously unpridictable so far as how
long they last. If you are on a budget, rebuild. If the account is fat,
buy new. If you can't decide, flip a coin. It's not going to
matter.....much. Well, it might, but there's no way of telling ahead of
time.... Sorry I can't be more specific....