22 760 air leak

Found an air leak on the engine on the driver's side. It's on something right in front of the spin on fuel filter. Not for sure what it is. Looked at another 760 and it did not have the item. Have pics attached.
Took it apart and has a cap, rubber washer and a spring type washer. Had some gunk in it, cleaned it and still leaking.
Doesn't seem to affect the air pressure while running. I've done several leak down tests and they are good. Sometimes doesn't loose any. Then one after may only use 1 or 2 psi.i can hear it leaking with the truck off. May leak down over night to around 40.
As a side note the truck has the ecs suspension and it leaks down when the truck is not running. Dealer says that's normal.
So any help would be appreciated to figure out the problem in the pics