If you are talking about this pic as the leak you are concerned about. It's not nearly as bad as it looks.
That is the breather cover. The streaks on the upper front of that cover look like radiator fluid, check the hose clamps above that area while you have the Tank off to rinse out the old gas, might as well take the petcock off and clean that up real good too.
There is a tiny little duckbill filter. It is inside the fuel line. Remove the fuel line where it attaches to the carb bank, and you will find that little filter. Don't remove it, but it does need to be cleaned. It's OK to add another filter between there and the tank if you want, actually that helps because that little duckbill filter gets clogged pretty easily.
The oil on the bottom of that cover.... Well when these bikes get dropped on the left side, oil gets into the breather cover. it then gets sucked up into the airbox, where it then drips out onto the sprocket cover.
So I'd check the breather hose, and clean out the breather too.
That small bolt just above the breather cover is the drain plug to drain the coolant from the block area. to drain the rest of the cooling system remove the bottom bolt from the water pump.