Filament (3mm) Guide for accessible Wade's Extruder

Derivative work of laser cut MDF guide for 3mm filament from Sacha Di'Angeli at PS1 (which I could not print) and of thing 13351, which needed a slot for easy access.
First attempt at openSCAD 2011.12.19
Could not figure out existing part 13351, so mostly started from scratch

This part is an attachment to accessible Wader's extruder, it is a guide for 3mm filament to prevent filament walking off guide bearing.
The primary difference from thing 13351 is the slot from the PS1 part, which