New and improved design. This iteration is 3 mm shorter than the previous.
I'm still getting some slight, unbalanced stiction when playing with the mechanism by hand, until it's connected to the motor. Once it's all fastened together the motion feels perfectly smooth, which is odd to me. My only guess is that the bearing support the motor provides to the sun gear is enough to fix whatever axial misalignment there is, so it's a non-issue...?