If you have the patience, try using Hondabond HT on that gasket (from the Honda dealer). The stuff is 10x better than any Permatex product. Also, make sure you let it dry for at least a day before putting water back in. I typically apply the Hondabond, finger tighten the part on, then torque it the next day as to not squeeze all the sealer out when it's still wet. Also, have you run that sub yet? I'm wondering if that bend at the end of the port will cause wind noise.