See here, particularly post #6
Post 8 is worrying but having done this procedure myself I honestly don't know how you could shear anything unless being really ham fisted.
The black round disc with the two holes is the thing that sets the stiffness. It's a reverse thread, so clockwise loosens it. Maybe this is how it could shear - winding it anticlockwise thinking you're unscrewing it but you're actually tightening it up with the leverage of a big piece of wood! I couldn't find a couple of suitable nails so I actually used a pair of circlip pliers, the ones with the round ends that open when you squeeze the handle. Just put the ends in the holes and twisted the pliers round.
Too tight and the wheel will be stiff, too loose and while the wheel will turn freely I found the wheel felt wobbly which I didn't like. It felt like the mechanism had no support. It took a bit of trial and error as it feels very different when you have the bits out to when you're actually using it.
I may be wrong I would have thought if you remove the o-rings you open up the mech for water ingress, and also the wheel would be wobbly.