In my MMU3, I was using a selector front plate that uses a PC4 M10 pnematic coupler, because I'm using a 3mm ID PTFE tube that goes into that plate, it was deforming quite easily and was blocking the filament from time to time. I modeled this new plate that has a nipple to hold the PTFE tube in place (as shown in the pictures), this helped immensely and I don't get “filament got stuck” error anymore.

This can also be fitted to the old MMU2/MMU2s models.