Although, being jig-made, the slots are probably in the same place on the two axles, the question remains: where exactly are they? The right-hand (red is always right in my workshop) end is noticeably off-centre, while the left-hand looks pretty good. Our eyes are fantastic at noticing things that are not straight or centred, but not much use at telling us the magnitude of the deviation.
For giggles, I tried to measure the difference with my calipers, but the chamfer on the end of the axle makes that futile. Instead, I designed and printed several strips of 3mm holes. Each hole has a wall across it to engage with the axle slot, and the slot is shifted .001″ from hole to hole. So on the first hole, the wall is centred; on the next it is .001″ off-centre, in the third hole it is .002″ off-centre, and so on.
Then, I simply press the axles into each hole in turn. Sometimes the wall will break, and sometimes the axle will shave a little material off either the wall or the hole. I continue to try holes until I find one that seems to require the least deformation, and that’s the winner.
Multiple trials lead to a consensus, and I feel the left hand slot is close enough to centre while the right hand slot is about .003″ off-centre. I then changed the 3D model so that the right-hand drivers have the wall .003″ closer to the crank-pin. The real trick will be to remember to orient everything correctly when it comes to assembly!
Pembroke:87 