I've started re-using the original red colored o-rings on the points/advance housings if they still look good (not all flattened out). On my rebuild, I used the black replacements that came in the Athena gasket set. They worked OK until I pulled the housings a few years later. They didn't seal back up. They were deformed, square shaped now instead of round. I'm thinking they are just plain Buna-N rubber and that doesn't have as high a heat rating as a red silicone o-ring would. The head is one of the hottest spots on the motor.