Yes, I agree with Peggy - protecting susceptible areas of the shell
from acid is a good idea.  I prefer vaseline ("petroleum jelly") for
that purpose.  I think it "stays in place" better than oil.  But you
can only apply it to the interior of the shell as far as your finger
can reach.  If acid gets into the upper whorls of the shell, beyond
the vaseline-protected part, it will be eating through the shell from
the inside, and you may suddenly find you have a hole in the shell,
even though you were controlling the acid action on the exterior.
 
Paul M.