RDG fan:
Chris [Lehighline] is correct. Although I've not seen FM motor trucks [post war LIONEL anyway] succumb to 'zinc pest', I'd never rule it out 100%; careful evaluation on a case-by-case basis is your best bet when purchasing items that you feel may be suspect. Although most early pre-war items [particularly frames and steam chests] are highly susceptible, because zinc die-casting was in its infancy in that era, there are still many that have survived; good, climate-controlled storage over the years helps to preserve die-cast items that may have otherwise fallen victim to 'zinc pest'.
AS far as later [post-war and modern] issues with 'zinc pest', well, there really should be no reason for it excepting laziness and carelessness in the manufacturing process; the problems with impurities and such have all been worked out and careful manufacturing procedures should have eliminated this issue long ago. I strongly believe that in LIONEL's case with the 1963 GG-1s, quality control was not nearly what it used to be ten years prior.
Alas, we don't live in a perfect world.
As an analogy: if I painted F-3 shells over dirty, greasy, non-primed material, you can guarantee the paint would not adhere; many folks realize that Lionel had issue with early 1948 #2333 New York Central F-3s which can often be found with flaking paint; the culprit for poor paint adherence is most often poor preparation. I learned long ago to thoroughly clean and prime coat everything we paint!
-Len Carparelli
