Hal, welcome to the Wonderful World of Pot Metal.  The inventor of this
impure die-cast zinc alloy has been cursed into Hell by more antique
collectors than anyone else in history.

But somewhere, in my boxes of papers I moved from Chicago to Maine,
is a four-page article I saved years ago from a model train collectors'
magazine.  A professional metallurgist with a rec room full of ancient
Lionels researched the problem and came up with an electrolysis
procedure that reverses the degeneration -- up to a point.  His process
fills metal back into the tiny intergranular cracks where the rot
progresses.

It strengthens the part and prevents (delays?) further corrosion.
Of course it can't fix parts that are already warped, broken, or
"exploded" but I think Hal mentioned that.  If anyone's interested,
I will add it to my mech-music agenda to try finding this article and
post the details.

Personally I think that lacquering a part to seal out moisture should
retard further damage, but it won't restore any lost strength.

By the way, a _good_ batch of pot metal will last forever, even under
moist conditions, and a bad batch will "explode" no matter how well the
item is cared for.  It depends on whether the impurities were lead,
arsenic (!), aluminum, or whatever.  Any of these may have been added
to the zinc to make it stronger and harder.

Hope this keeps your spirits up!

Mike Knudsen