The filamentguide.stl has one layer of material in the guide bore which has to be drilled out to open the pocket. This layer was needed as support material to ensure proper printing. The nosupport-Version shows the pocket without support material.
I stuffed a sponge cloth into the pocket and damped it a bit - works like charm.
(My printer still has some calibration issues as I didn't build it long ago so don't wonder at the gaps in my print...)
Designed using FreeCAD and printed with silver PLA from GRRF.