Re: oil in headcase?
It's not uncommon to find that oil residue in that area of the motor. It's from fuel that has leaked out of the carbs. Sometimes when you tilt the motor all the way up, fuel will leak out of the fuel bowl vents in the carbs.
It could also be the result of a leaky gasket on the carbs, or a bad needle valve in the carb causing too much fuel in the bowl and leaking out of the fuel bowl vent.
To check for carb leaks, drop the motor down to it's normal running position. Take the engine cover off so that you can observe the carbs. Squeeze the primer bulb on the fuel line 4 or 5 times. The primer bulb should get pretty firm. Look at the carbs and see if you see any gas leaking from them. If no leaks, you should be OK.