This thread is really hard to watch. I've seen zinc pest with most of the major train makers new and old. If the mixture and casting temperatures are not right, it sets up sites for future corrosion. You can go back to Ives tenders in the late 1920's, most of anything that McCoy made with zinc alloy castings, and now examples from all the major train makers, MTH, Atlas, Lionel, Williams, KLine
Jim