You could have a small crack in the head or the leak could be coming from the stud that the dizzy is mounted to. (If that is how it is mounted) Remove the stud and see if the other end protrudes into the head itself. If it does, degrease the whole lot and refit stud with stud lock or thread sealant.
Bear in mind I do not yet know the 16V, so I could be talking out of my @rse!!!