I know what material NOT to make the MMU3 out of
Polycarbonate.
I thought I was doing myself a favor by using a high temp resistant, stiff material.
Instead, I am having a grand time getting all the bearings in place due to the stiffness of PC. I now miss the flexibility PETG has, but am almost done with assembly. And the skin on my fingers.
RE: I know what material NOT to make the MMU3 out of
Did you use PC-Blend or PC-CF? If you used the former, you will also struggle with dimensional stability as PC-Blend warps with larger parts quite a lot, it even warps to some (even though smaller) extend when using relatively warm chambers at 60°C. (I think it would need at least 70°C or so, to minimize that issue).
A better alternative would be probably ABS or especially modified ABS like Formfutura TitanX or 3djake NiceABS which can be printed with high dimensional accuracy and low warping, retain some flexibility (not quite as much as PETG but much more than PC or PLA) and are pretty thermostable too.
Mk3s MMU2s, Voron 0.1, Voron 2.4