HI. This will be a basic cylinder head issue concerning the gasket in that particular area. The gaskets have failed; possible rupture or severe crack. Now, this may also be a cracked head(due to over revving). Make sure to inspect the structure of the head,carefully for any structural damage. I do not suspect this issue, but i would advise to check for this serious condition. With that being said, replacing the head gasket should correct this issue and properly seal off the cylinder sector.
Additionally, If you want track the leak properly, here is a very easy way to do this. Simply sprinkle talcum powder over the top of the engine and go for a short ride. Once the powder starts to warm and mix with the spilled oil, it will expose the track, thus leading you to the origin of the leak. These additional areas of concern will be:
The spark plug tubes- These tubes have been known to wear through with slack cam chains.
The Cam Plugs- The cam plugs on top of each cylinder can cause this as well.
Valve covers- Check them thoroughly.(this may be the lone culprit) failed valve cover gasket.
- NOTE_The spark plug tubes will screw out with a suitable sized tube spanner. This will only be relevant if they are filling up with oil.The cam plugs will leak, overtime. Its a big job to replace them, you will need to disassemble the engine to get the heads off.It is possible to slow or even stop the leaks by cleaning the edges with Isopropyl alcohol cloths and forcing high temp silicone sealant into the seams with your finger tips. Let it stand for at least 24 hours to cure before starting the engine.