[@NecroKnight]

Well any stored equipment wouldn’t just be left out in the rain, it would most likely be sealed in storage, or somewhere safe from elements. ( beside the point) 

You don’t exactly need to be an expert to use a tank, anyone and hop in a figure it out. ( how do you think they do it in Afghanistan?) chances are, there is someone that knows how to do most everything you can think of. I can’t believe that everyone would be completely ignorant. 

This is also post apocyltia, you shouldn’t be manufacturing anything. Nukes are big and destroy cities, burn out electronics. Industry is target priority one during war. If anyone has any industry left, it’s either makeshift or very well hidden. That being said, you will be canibalizing parts from destroyed equipment. 

People would get better at scavenging and fixing equipment in a post apocalyptic world, since there is no other choice. Even if a destroyed one is sitting around, someone will see it and wonder “ how does this work”