I believe Roper-Whitney owns the Pexto line now.
Is your shear a flywheel type mechanical shear where the "switch" is a footpedal that trips the clutch? Or is it a converted stomp shear using air or hydraulic cylinders? The reason I ask is because the great majority of Pexto shears are converted stomp shears, and if that's the case then the simplest thing would be to replace the entire foot switch assembly. On the other hand, many flywheel type shears have either a brake assembly or a dog mechanism, depending on the size, that stops the shear at the top of the stroke after each actuation. These can be tricky to adjust, and you definitely wouldn't want to proceed without the correct manual, because if things get out of time the shear can do lots of damage to itself real fast. Some mechanical shears also have a lever that can be moved to provide either single stroke or continuous operation. We had a Wysong for a while where this mechanism was loose and drifting back and forth, causing the shear to single stroke at times and to stroke continuously at other times.