Bummer is right on the stripped plug and seat... I have never had that problem ,in such as important area ,yet anyway. I would ask a good mechanic about that. Do be careful if you use a tap or thread reamer/cleaner and a new plug- I'm speaking of metal fragments internally from the tap.
I would consider the tap option and new plug if it were me but I live by the seat of my pants sometimes on decisions . I have fallen off (really with) a 16' ladder that I knew was dangerously placed , walked away from a serious wreck , heavy equipment encounters ...angry cow encounters, and still I am here. I give thanks to the Lord for all of those and getting me through my RTV's redos too . No joke. When I have a problem I will sleep on it and say a prayer and when I wake up , the answer is usually before me.
Let us know how this turns out for you. bordercollie