Help me ID this sensor!

[mrian]

I have a hunch I have an oil leak from a sensor on the right side of my 2003 2.7 engine. I do not know what the sensor is for, and I need an o ring for it. It is located immediately behind the most rearward coil pack on the right side of engine, visible easily from the wheel well with the wheel removed. It has a retainer with 2 bolts holding it on, and what I presume is a groove for an o ring, mine had none installed. I added images of the sensor location, and the spot where I think the o ring should be, but I would love some help!