Older Nockovers have a S shaped link between the paddle and the faceplate, held on with a kind of starlock washer. Later ones have a pair of steel strips with pins.
We change the pins for M4 stainless bolts with washers and M4 stainless locknuts. If any of the older type have the starlocks pop off due to corrosion we bin the S link, make new stainless strip links and fit stainless pivots as above.
Nockovers have the advantage that they fall to about 45 degrees and then stop, so when the reset string is pulled, the tension resolves into an upward component to lift the target. Gamos and other makes like Umarex tend to fall almost flat, and then the string tension acts to pull the whole target towards you rather than raise the faceplate. We modify Gamos by putting in a limit screw that stops the faceplate falling beyond the 45 degree plane, and that has cured most of the broken string problem.