It's the oil pump gasket, I can see it bubbling out behind idler
It also collects down in pulleys and sprays all over, I think I will do crank seal while I have the pump out. The odd thing is the bolt holding in the old idler was a long 6mm bolt. The threads in the back of the idler/head are 8-10mm. So someone either lost the bolt or messed something up, and threaded a longer one in. Not sure what to make of that.
Hard part now is finding an oil pan gasket for less than $50 shipped that can come in a reasonable amount of time.
Does the crank seal get pressed in oil pump housing from behind? Thanks for linking the writeup!