Cylinder misfire, rusty spark plug (with picture). Diagnosis?

Engine: 5VZ

Guys, I pulled a code indicating cylinder #3 misfire. I figure I would replace all spark plugs since I just bought this truck with 165k miles. When I get to cylinder #3, it looks like the threads are rusted. All the other plugs have shiny threads. See the image to compare. The left spark plug is from cylinder #3. Also note the discolored ceramic below the electrode vs the white ceramic on the other. What do you guys think? Should I be more concerned about other issues or should I replace the plugs and move on?

Thanks

 

You may be getting water into the cylinder from possibly a bad gasket, a broken water jacket, etc. Or it could be as easy as a plug that was loose and not tightened down all the way allowing exterior moisture to seep down the threads

 

do a compression test.those trucks are known for ceacked rxhaust manifolds.If left go will damage exhaust valve seat,(ask me how i know)