Hi, I had an idea for a different filament guide...

It can be used if you have an external filament holder (I haven't got one yet).

The spring can be found by searching for: "Cord Management for Roller Shutter/Roller Shutter Cord" or "Line Guide for Roller Shutters with Upper Deflection and Cord" https://www.amazon.de/-/en/Guide-Roller-Shutters-Deflection-Spring/dp/B00TM0QGIO/

The spring I used has a diameter of 9,9mm and is 250mm long.

The advantage is that the spring pre tensions the filament the whole time which should work like a "filament buffer". I splitted the part for easier printing.