Before diving into the details, these individuals should be mentioned based on their contributions to support this project.
Original designer/creator/inspiration: CG-Tech
MK3S & MMU2S Models: jzkmath
CG-Tech had the initial concept of the cooling fan assembly for the Prusa MK3, that has slowly progressed into different remixes enhancing the design to add rigidity and bolted connections to the extruder assembly. I helped contribute to the bolt on design for the MK3 version and was itching to create a similiar version for the MK3S. However, I wanted to include the ability to further the design by adding a secondary set of users that utilize the MMU2/MMU2S which encompasses a different filament sensor cover. Uploaded are four files, you will need two depending on your version (whether or not you have the MMU2 or standard extruder).
The difference between both designs are simply the different filament cover, and the number of bolted connections to the filament cover. Due to the size of the filament cover for the MMU2S, only one bolt connection was able to be included. However, the standard MK3S has two bolted features. Regardless of the difference, the bolts should be sufficient enough to prevent movement. Due to the bolted location, you will also require supports for this - but very minimal.
I am setting this as a work in progress until I can validate the design myself, and if someone could validate it for the MMU2S as I do not have that configuration. If you are curious how I hooked up my cooling fan to the EINSY board, I used a Noctua NF-A4x20 fan that is routed to the 5V rail located below the reset button on the EINSY board.
MK3S design validation completed. I finally got around to upgrading my MK3 to MK3S. I printed it out, supports came out pretty easily. I first attached the filament sensor cover to the cooling fin using M3 10 mm bolts (5 mm would probably been okay as well). I then mounted bolted the filament sensor cover assembly using the original screw. It fits perfectly! I have added photos of the retrofit to the thing.
Shout out to AJMaun6945 for completing the trial of the MMU2S version of the thing! With that being said, there were some initial design issues with the fitting. Please refer to his remix for the MMU2S version. I will keep the files up for reference, but please use at your own risk. The regular MK3S version has been verified and remains valid.