oil get out from 1 of the 2 vaccum line below the bike (downside the exaust)

after riding the bike I see a spot of corrumpt oil (very black and gummy) that comming out from one of the 2 vaccum line below the exaust pipe .

what is it %?
 
they are connected to the gas tank -- one is an overflow hose and the other is a breather. Possibility of gas coming, say after a full top off, and just picked up some dirt that has grown since your last cleaning??
 
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