Kinda hard to see what you are referring to... The dark black bolt? If so, I am pretty sure that bolt is bolting that ground cable to the engine. I don't think it even seals any oil in the engine.
What is probably happening is oil from your engine air filter is dripping down from the airbox onto the engine. Not to worry, mine does this too after I put too much oil on the air filter. But just to be sure, take a rag and spray on some degreaser, and wipe down everything inside that area, including the oil you see. The engine and the airbox. This way you can see if it continues to leak.
Then if it is actually from the air filter (which has oil on it by design) you probably just need to open the air filter slot on the side of the bike, slide the filter out, and clean the inside of the airbox with a rag, and wipe down the excess off the filter.
If I am totally mistaken, could you take more photos and add some circles or arrows to point to exactly what is leaking and where the oil is going?