I used another persons solid coupling & found it made a difference, but the 8mm shafts wouldn't fit & caused a little wobble on the leadscrew. I have now, from scratch, designed my own couplers which are now being tested.
These are smaller than OEM & you don't need to be a Gorilla to do them up so the shafts don't spin in the coupling.
Under testing at the moment.
Decided to do this as my lithophanes started to have regular banding, but this could just have been the different brand of filament (PLA) I'm using, Had issue with just this brand.
Real Filaments PETG
Top/Bottom layers = 8
Outline/perimeters = 2
Do not overtighten & clean out holes with 3.2mm drill by hand.