I was having the same problem with mine and had decided to replace the vent hose. I dripped all the time. I went to do the work and was surprised at the great condition of the hose. So I decided to give the fuel cap another try.
This is my third. And miracles of miracles, the problem completely went away. No drips, even full to the brim. When I compared the new cap to the almost new cap, I realized the manufacturer had put the gasket on upside down. No wonder it leaked! Now it is reversed and saved as a backup. My 3 year old problem is finally gone.
Hope yours is that easy. Mine was giving me fits. Now, all is right with the world.
2003 Alpine 40FDTS (400HP)
Long Beach, CA