Leaking Hydraulic Manifold/Distro-Box

[mekkerlc]

My hydraulic 4-slide system is plumbed to a manifold, or distribution box, which allows me to turn off, or adjust timing, of each slide-out.
The adjustment is made with small, black, twist/screw 'knobs'.

Where these 'knobs' screw into the manifold, it has been leaking hydraulic fluid...very, very little, but enough to dampen a paper towel I wrap around them. These leak even when the rig is just sitting.

Has anyone experienced this?

Have a repair idea?