there was a topic on gearbox running rough/tight on here not too long ago, and there it was pointed out perhaps the shaft is flipped in orientation; and indeed it was.
without reading KTB and instruction sheets, it was visible when juggling around with the gearbox parts there was one end shorter than the other, and when fitting the gears it showed clearly which orientation is the correct one.
wouldn't surprise me if the shaft itself is symmetrical, and the 2nd step is grinding the stepped diameter to the required length.