MMU2S Extruder Filament Sensor Micro Adjuster

Update: This part was recently changed.  If your extruder was manufactured after February 2021, you should use the 2021 version.  Earlier printers will have to use the other.

I found it very difficult to set the very sensitive extruder filament sensor for the MMU2S multi-material accessory. I would get it set perfectly but as soon as I tightened the bolts it would be off.  Shifting it the tiny amount needed to compensate for this movement was very difficult. This is a modification of the OEM part which simply adds a slot for a square nut and 20mm screw. This allows you to set the alignment very consistently. If you need to adjust, you just loosen the bolts turn the screw a half turn in the desired direction, snug it up, and re-tighten. It made a world of difference for me.  It is also very easy to install on a stock printer - only three screws to remove to replace the original part.

I also elongated the slots a little to give more room to adjust for any drift that may happen over time.

P.S. If you are having difficulties with consistent FS operation, you might want to consider this other mod:

https://www.prusaprinters.org/prints/5426-reinforced-mmu2s-extruder-idler