Just put a used motor (3,7l) with 31k miles, from day one notice a small leak, searching on internet about it, found this forum, so just read the thread about valve cover gasket, and many ppl said some times are loose nuts around, so today i decide to take a look and i found a small crack on valve cover.
So, I have to change the valve cover, question is, can i reuse the gasket or not? if yes what kind should be the best? and where?

 

I would replace the gasket as a safety measure to prevent it from leaking after.
Rockauto.com might have them, Local part stores might have them, I cant see them costing to much