That's a very new Mariner, that's the latest version of their hinge, with the lever aft when closed. Earlier versions of that hinge have the lever forward, and that is my Dahon hinge, circa 2005 I think. So I don't know the internals on your hinge.

On mine, I did two things to improve the hinge.

1) The screw adjusting barrel had nothing to lock it in place; I added a thin nut on the male threaded portion, to lock the adjusting barrel in place. Otherwise I was adjusting monthly.

2) I improvised a Deltech style cable, this changes the forces at the hinge from bending, to compression shear, less stress on hinge, stays tighter longer. Does your Mariner have a Deltech cable? Dahon has been running hot and cold on Deltech, first on, then off.

Since the above improvements, I haven't needed to adjust my hinge in almost 3 years with a lot of riding, not a touch of looseness.

I'll look for feedback on the above, before more info.