Alright, I'll be serious for a second. Remove the derby cover, buy a new gasket and torque properly (sequence and values). If you are talking the whole outer primary, sorry but the same advice. Although I might go around it once with a torque wrench, but wouldn't hold out much hope. In my experience (mostly aviation), just tightening things up is generally ineffective unless it wasn't tightened properly to begin with.
Are you absolutely sure it is your primary gasket? Only reason I ask is because I thought mine was leaking. Called the guy that works on my bike, He is also a good friend, told me that it was more than likely the primary shaft seal and that it was just drooling down and making it look like it was the gasket. From what I understand, it is not very often that that gasket will leak. Just a thought.