What brand is the loader valve?
What you are pointing to is the pressure relief valve. Its what you adjust to set the system pressure.
Where exactly is it leaking on that valve cartridge? Because there is an o-ring where it threads into the casting of the loader valve itself. That could fail.
But if its leaking around adjustment screw your arrow is pointing to, something inside the cartridge has failed. Sometimes they can be disassembled and rebuilt, sometimes not. IF you know the manufacture and model of the valve, or any info stamped on the cartridge itself, its usually easier to just get a new relief cartridge as a whole.