there is normally no adjustment on the clutch slave push rod. its an all-hydraulic system, so it does not need adjusting. if the clutch slave cylinder is not pushing the gearbox lever far enough to properly disengage the clutch, then it has a problem with either leaks or lost motion in the pedal/master cylinder. this is what you fix first. The pushrod coming out of the master cylinder usually has adjustment to take up free-play in the clevis, pedal bush etc etc. Get an assistant to watch the slave cylinder while you push the clutch pedal. You want the slave to start moving after about 15-20mm movement of the pedal rubber The Sportivo box is like most other C type gearboxes , their clutches are usually very robust, but the gearbox syncros are terrible. The faster you spin the box, the harder the syncros have to work to slow down the gears spinning around inside. The slightest bit of clutch drag (poor disengagement), will make the job of the syncros almost impossible. Diagnose the fault!!!