First you need to make sure of where that drip is coming from. Naturally it's going to end up hanging from the lowest point but it might be coming from somewhere above. I'd suggest you clean the engine case with a solvent, ride the bike around the block then inspect the engine carefully to see if the oil is actually coming from the case gasket or somewhere else.
It isn't unusual for a case gasket to leak and sometimes it is from a loose case fastener. However I'd be very cautious about overtightening. That is only a 6mm screw and exceeding about 60 inch pounds of torque could break it and leave you with much bigger problems than a small drip.
Tom