A lot of the mysterious oil leaks come from a little hole on the rear of the rear cylinder and the same hole on the front of the front cylinder. These little holes are the exit passages from the deep set spark plugs on the left of the front cylinder and the right of the rear cylinder. They are there to drain any water that might get into the spark plug tube. Each of these spark plug tubes have two o-rings that can go bad. If one does go bad it can let water into your oil or oil into the tube which then drains out the passage. It's an easy fix once you get the replacement o-rings. Try BikeBandit for the o-rings.
Part #'s 92055 31mm & 92055B 27.7mm You need two of each. Might as well do all of them while you are at it. The rear axle nut fits the spark plug tubes to remove them, just unhook the plug wire put nut into recess and use a wrech to unscrew. You don't have to remove spark plug itself unless you want to. This would be the most likely cause, easiest to fix, and cheapest. Any questions, give me a shout.