well, I dropped 3 valves in that cylinder 2 years ago. After putting the bike back together 2 months ago, i'm guessing the heat build up caused previously unseen weaknesses from blow up to to magnify.
I must be missing something here. Are you referring to the scratch on the cylinder bore? That isn't going to cause coolant and oil to mix. A problem with the deck surface, head gasket, or oil cooler will cause coolant and oil to mix.