Vintage Ken Mohawk Twist and Turn Waist Several Marks on Him Mattel 1968 C63

Vintage Ken Nude Doll Twist and Turn Waist, Several Black Marks from lots of play. His back is labeled Mattel 1968 and he has C63 on his head. Someone wrote their initials on the back side of his underwear you can see in pics. I tried rubbing alcohol to get the black marks and initials off. It almost got the initials but didn’t touch the black marks