You may be on your own. Bachmann is generally unresponsive to customer emails. I purchased an SD-70 last year. The True-Blast Plus sound card failed right away, and Bachmann wouldn't even respond.
I see a lot of zinc rot on repairs that come into the train store where I work. Mostly modern era production. But every once in a while, I will see postwar Lionel castings that swell up with zinc pest and disintegrate.