Tiger, if you a convinced the gasket is a problem and you want to reseal it then yes you would need to split the cases. What I did with an old Enfield twin a couple of years ago was to go around the crankcase join with a hacksaw blade and dug a small grove around it and then put a bead of JB Weld in the grove and that was enough to seal the cases up and stop the oil weaping out. Could be worth trying but personally I doubt that would be your problem
