I had two different oil leaks that originated where the breather hoses connect to the spine frame that were similar to yours. The first was at a fitting on the right side of the frame (under the gas tank). The factory installed an incorrectly sized washer that let oil leak even though the bolt was tight.
The second was caused by a loose oil clamp on the hose behind the steering head directly under the frame. I had to remove the steering damper to tighten this one. It seems that oil can travel down the outside of the rubber hoses or along the bottom of the frame and collect on top of the engine (directly under the throttle rod) or on the ridge of the oil pan.