[horsa]

Attached a shot of my oil cooler lines even though its a different setup. Yours appears to have a second breather on the driver side of the rear engine. I've got that part connected to the top of my differential and don't have another breather on the engine other than the one where the oil enters the engine at the fuel pump where you are having the leak.

From your routing, the by-pass is open and sending the oil to the upper line. It's leaking is probably related to either the engine having too much internal pressure or air is coming in from the second breather and exiting from the higher original factory one and causing issues with the oil trying to flow inward against it.

Not real sure what the purpose of the alternate oil route would be since I've never seen that on another vehicle so far. If it was providing essential oil, they wouldn't have made it only functional when the valve was in by-pass mode.

Can you open the lines up front and confirm that oil will flow from the oil cooler lines? Or do you have the oil cooler shut off by manual lever if still installed? I don't have the levers on mine so can't turn them off if I wanted to.