If you do a search on this site you will find more information.
I have seen this before, the oil leaks from the inside of the motor and travels down the engine bolt that passes through the block.
If you look at a cutaway of the motor you can see where it all happens.
I think most just learn to live with it.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.