Prusa Mk3S MMU2S Tower Print Buffer recomends at step 3 to “cut the existing 10 aluminum buffer roller tubes to 10.5cm long”. Instead of cutting,  you can print this spool shafts (print two 111mm shafts for the center spool and the 4x2 109mm shafts for the side spools).

Printing settings:

• seam position random
• fill density - 15%
• fill pattern - triangles
• 3 perimeters
• for stability, enable outer 10mm brim with a close to zero separation gap (0.1mm worked for me)