This reminds me when I thought I had a leak on my high pressure line going in the steering box. Wet all around the fitting where it went in the box. Got a new line, it still leaked. Changed the line again, it still leaked. Finally found out the pump was leaking around the seal behind the pulley. The oil ran down the front of the pump, made it's way to the rear of the pump and at just the right place, it dripped right onto the fitting on the power steering box. That was very frustrating till I figured that out.
If you can clean it up really good, maybe you can sit there with the engine running and make sure it is leaking from the sensor.