The splines are the serated ends of the bar (male end) and the serated interior of the turnbuckle (female). The turnbuckle should not slip around on the shaft, because it has splines. If you need to turn the assembly you can separate the two and move it around one spline at a time and slip it back on, alhthough there is a limited amount you can do this because the lock bolt has to go through the flat spot on the shaft. If it was working OK previously, I would suggest initially just sliding the turnbuckle in or out a little on the shaft, this woudl help to recenter your gear shift. That is all mine came down to, although it was a bit of trial and error to get the exact right spot.
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