Debating between rebuild and replace

I have a 2013 Subaru Legacy 2.5. Check engine light came on driving and the dealership told us it was a misfire in cylinder 3 as well as ‘random misfire’ codes. They pulled #3 and it was covered in oil. Knowing that, I’m wondering what testing I can do to figure out if it’s serious internal damage or if it stops at the valve cover gasket. Thank you.