I believe it's the oil pressure sensor under the intake manifold, near the coolant lines. Edit - are the threads supposed to show?

 

if it is not leaking, don't touch it.
The bolt on the switch is cone shaped anyway.
But it looks a bit shallow screwed in tho...

 

Heres a thread that discusses the repalcement of the EvO8 pressure sensor. The EvO9 sensor is at the oil filer housing so the thread states
https://www.evolutionm.net/forums/ev...re-switch.html

Likely your sensor was replaced & wasnt fully seated. As noted, if its not leaking, might be best to leave as is

Heres a pic from the thread

 

Ok, thanks guys!

 

pipe threads don't screw all the way in they are tapered.