Mystery revealed: In the earlier photos, the left cap is the original Model F cap and the right is the new test cap.
I also posted information on the grease mod on my web site blog:
https://www.modelfkeyboards.com/a-quieter-model-f-keyboard-how-to-reduce-mod-the-sound-of-your-model-f-keyboard/Copied below:
In addition to the floss mod described on the Geekhack/Deskthority keyboard forums, another mod to consider is the grease mod, researched and described by the below YouTube user. Also in my research I have found that pressing the springs down all the way on the flipper (normally there is a 0.2 to 0.3mm gap) reduces the ringing. I do not offer and have not tried any of these mods but below is some information to consider.
The purpose of the grease mod is to reduce the reverberation/ringing after each key is pressed.
His comments are copied directly below.
Apply Synco Superlube on the inside of the spring with a metal probe…just enough to dampen the vibration
As an experiment, I tried a few switches on an XT F. I did nothing to the first XT F in the video…you can hear the sound I’m referring to…it’s like a super-loud, much more intense, sharper and “drier” version of what my (in superb condition) 1988-1989 Model M boards sound like. Then on the second board, I did the Alps spring lube trick on the keypad only. The feel is the same, the click sounds great (to me), the actuation force is ever so slightly less. But the annoying (to me) spring noise virtually disappears.
video 1 – detailed key sound (lubed keypad; unmodified other keys):
video 2 – typing demo of the unmodified F:
video 3 – typing demo of the fully spring lubed F:
