Today I learned the process of how to create a seamless texture using a standard image. Here is how I did:
This is the original texture I found on the internet for a scratched up metal.
Here I cropped my texture to a 1024x1024 square.
I offset the original square, blending the edges using content aware fill and healing brush.
And here is my texture tiled a couple times! Not all that great, but it doesn't have any harsh edges that would be obvious in the game engine.