Summary

An Improved Filament Guide
I just received my Prusa MK4 and find it a wonderful machine indeed. It is faster and much quieter than my MK3, and produces parts that are beautifully smooth and precises. I use it to print test apparatuses in my laboratory, and small printing ridges can be the difference between a functioning part and not.
I was impressed with the filament guide idea, since a fresh roll of filament occasionally will jump off the reel on my MK3. But the design is seriously flawed. As supplied, it sits over the top of the roll, so it causes a maximum bend to the filament of about 30 to 40 degrees! This required Prusa to insert a Teflon ring due to the acute friction that causes.
So, using their notion of guiding the filament, I made some changes.
1) This guide does not need to be screwed on, since it slips over the lowest arm rib.
2) It also has a small slot in it, so the guide can be threaded after it is loaded in the print head.
3) The maximum bend of the filament is about 150 degrees. Remember that no bend is 180 degrees. So, no Teflon is needed since the filament barely knows it is being guided.
Included here is the gcode for the MK3 and another gcode for the MK4. I have tested printing on the wrong printers, and both work on either printer (after the printer asks to proceed or not), but I include both anyway.
If you are printing something that is very tall, you will need to slide the guide up higher. It will slide onto any of the support ribs. I have been running my design for over 20 hours of printing time and it works just perfectly. Thank you, PRUSA, for the notion of guiding the filament.
Also included is the CAD image and a picture of it in use. My MK3 is named “Jolene” because my wife tells me the I spend so much time with her, that she is the “other woman”! LOL