I told my brother that some one on this board could help us identify the unit in the photo.This is a photo from underneath on the driver side next to and above the oil filter and oil cooler sandwich adapter. Its on a 1987 Chevy TBI 350 automatic. Suburban ,2500 ¾ ton 4x4.There is oil forming at that location but is just enough to leave drops on the ground and cover the under side to some extent and still we are unable to locate the exact spot where its leaking. What is the unit in the photo? It looks like a in line filter but has wires coming of the top. It seems that oil drops form on the bottom of it.Thanks

 

Oil pressure sender for the instrument panel gauge, and or light.
you may need to tighten it, if you replace it don't use teflon tape because it only has one wire the return signal connection is from the body of the sensor to the motor.