I'm not sure what the question is. The Doc is right, use MB black silicone sealant and it works quite well if the procedure is done correctly. It sets a bit quicker than RTV black so the work needs to be done more quickly so all is in place before it starts to skin. As for the head gasket, used to love doing them. Made a bit of money doing it. Could do two a day with a long lunch. Ask Doc, I'm sure he did a couple.
Bill