I didn’t find this elsewhere, so hopefully it’s slightly helpful for someone who has a 3D printer or has access to one.
After making the well-known O-ring mod to the button on my FW3A, I found it was harder to accidentally turn on, but then the button became really sloppy and tilted every which way. It also started to make this scratchy-squeaky sound that sounded and felt horrible. It was the same for steel against aluminum and steel against titanium.
I decided I should make a gasket that “pre-loads” the metal button, pushing it away from the cap and tightening it down against the boot.
It took several trial and error runs as I had to size the STL file up or down a few percent, but I found printing a single layer at 0.12mm makes a good gasket that lays right on the brim of the button, shimming it down against the rubber boot and making the button feel nice and solid.
Troubleshooting: aside from the wrong diameter causing fit issues, thickness needs to be within tight tolerances. Too thin, no effect on the button feel. Too thick, flashlight malfunctions as the button is pressed prematurely when the tail cap is tightened.
Not pictured here, but I also printed thicker gaskets to prevent the clip from spinning. Like many people, my newbie hands broke the clear stock O-ring. These clip gaskets were printed in brighter colors to make a nice hint of color against the raw titanium. I can stack different colors when going clip-less, leaving no gap under the tail cap.
These solutions might only serve a niche function, but it made my FW3s really awesome to use. Please let me know if you want the STL files or more details.