I do not know whether this is normal/OK but what I have found however is that some aftermarket sprockets have more play on the splined shaft than the OEM sprockets. I measured difference on aftermarket compared to OEM and found 0.2mm difference on spline channel width measurement, and this small ammount makes quite a difference to play on sprocket. I also suppose that if there was no clearance/play it would become a press fit which it is not, so limited play(small amount) should be OK but if sprocket is worn, replace it anyhow. If the shaft is worn, you should on close inspection see the splines are indented(sides of each spline no longer parallel where sprocket lies/fits) Hope this will help.