A couple days after I bought a Sofirn ST2, I realized that the hinge had stopped ratcheting and turned loosely.
This was after a weekend of rotating the light back and forth (as one does when fidgeting).
Unfortunately, this meant the head could no longer securely stay at the angle it was turned to.
Accessing the hinge took some experimentation, as none of the tools I tried could really grip the flat black cover.
Teardown
I ultimately succeeded by wiggling a cheap pocketknife into the gap between the cover and the light, prying upwards, and then working my way around the edge until the entire cover was free:
This really scuffed the aluminum, and nicked the o-ring slightly. Most of the resistance seemed to be from the o-ring which sat tightly in a groove - so at least it should have good water resistance.
The fix was easy: the screws holding the ratcheting mechanism down had come loose, likely due to the repeated vibrations.
All they needed was to be tightened up! But not too tight, since that actually makes the mechanism a bit stiff.
After squeezing the cover back on, the hinge felt as good as new!
Thoughts
I would recommend Sofirn lightly glue/threadlock these screws during installation, so they will not loosen through normal usage. This area is not easily user-serviceable, and some users may pursue a return/refund rather than trying to crack open the light themselves.
I will be putting the light through its paces, and if it loosens again I will reopen it and apply threadlocker myself.