Auto-centering shaft coupler
This is my attempt at reducing z motor oscillation. Instead of a single clamp this shaft coupler uses two parts which zip tie together, centering each shafts into 2 triangular slots on either side of it.
I've yet to finish my Prusa to really test this out but from initial testing this looks to give a decent improvement over the original coupler in terms of wobble-reduction without any major reduction in axial holding force.
The new coupler does have some difficulty fitting into the Prusa Mendel's motor mounts so I've had to drill mine out for it. It should not be too difficult to change the Prusa mounts to accept the new coupling.