A wrench at the dealer I bought my bike from showed me a trick. He would run a bead of grease with his finger on the bottom 1/3 of the derby cover hole. When the cove is installed wipe of the excess. The grease creates a seal.

 

Just a suggestion...if you are changing inner primary seals there are two very small COUNTERSUNK screws which hold Alternator Cable to side of crankcase,just before it exits to the 2 Pin Adaptor Connection. It might be an idea to order 2 new ones before you start the repair. Sometimes they are difficult to remove as they are "allen" type screws and if they have been off before they may have been "butchered/rounded" slightly. These 2 screws have to be COUNTERSUNK (H.D.Items). If you try to use a substitute, ie. small round headed screw, the "round" head of the screw can rub against the edge of the Alternator Cover/Rotor,as I found out when using round headed screws. Unfortunately I had to strip everything down again to find out what the "rubbing" noise was and found the round screw heads chewed. Good idea to add a touch of Loctite or similat to the screws when re-fitting. Bungo.