Advice / pointers on replacing valve seal

So I guess I got my first taste of oil pushing past the seal today. As soon as I pulled out the car started backfiring and running very poorly. Just pulled the #3 plug ehich is supposedly the culprit & kinda surprised how it looks. It's defintly looks beat up with lots of black carbon but I was expecting to see more of a wet plug. I did pull it a good 5 hours later though