First things first. Nothing will work if the joint is moving. Can you cause or feel any movement when stressed? Any at all? If so, joint needs to come apart, get cleaned up and reassembled. When cleaned up, you need to try to preserve the close fitting parts, so be careful. To get the bungs out, start with a course screw dead center in the bung. If the bung hasn’t been epoxied it will come right out when the screw bottoms on the head of the screw holding the joint. If the doesn’t work, use a Forstner bit perfectly positioned. If it were me, I’d epoxy it back together, including the artificial channel.