Koni Yellows, adjustment knob doesn't turn...
 

Got em on here, 3 are fine, one not so much, stuck at softest setting (by the feel). So, It needs to be serviced?

Pretty sure having one serviced costs as much as simply buying a new one.

EDIT: Derp, have to buy them in pairs so nvm.

thanks, you are spot on. called koni, if shock adjustment is hard to turn or doesn't turn the shock needs a rebuild or replacement. couple of authorized places rebuild (not Koni anymore) but unless you want custom valving it is cheaper to buy a replacement. singles or pairs can be ordered, going rate today for rear is ~$145ea. shipped.

Means the shock bottomed out hard and the valve got damaged. If the adjustment is set at the correct setting you can ignore it. That is what I have been doing with one of my rears.