"C" battery powered engines

I took some of my engines out of storage to run after a very long time, and two engines in particular I find barely move - Plarail 2003 James and Fisher Price circa 2012 Gordon. James almost runs fine, but will slow to a crawl and eventually stop. Gordon is worse. I've tried giving them the "love tap" (hitting them wheel side down on a hard surface, which usually works) but to no avail. I've even tried using "AA" batteries instead of "C" cells. Are they just, dead forever? Is there any kind of fix?