That doesn't look like it's done from a previous owner. That's the way they come from the factory. I don't know what the stuff is called, but Jeep seals all the seams with that coating/sealant stuff.
Here's a pic of my 97 Wrangler. I just painted the tub Khaki, and you can see in the seams, I have the same kind of coating that was like that from the factory