Don't crucify me, but I'm actually starting to believe in the rust module (no idea what brand/model#) in the Corolla. That pesky boulder that hit my hood scratched down to the metal, and I haven't touched it for months now...nary a sign of rust.
...of course, this is where ya'll say "wait for the winter."
...to which I reply:
the warranty will cover it any way (I read the policy - mine (at least) does cover rust from damage, as well). So, let it rust so they fix it and I don't have to pay for it!