My current earliest IBM Model M based keyboard, and one of the earliest Model Ms ever recorded! Whilst the overall assembly design 'language' is clearly Model M, there are some unique features to such early IBM Wheelwriter 5 (and Wheelwriter 3 and Quietwriter 7) keyboards including O-rings around each populated buckling spring barrel and 'cushionless' flippers.
See my website for more info on Model M family keyboards and buckling springs!
I am aware of O-rings’ impact in keyboards that use MX switches, having used some in a few builds.
It never occurred to me to use O-rings in my buckling spring keyboards.
How do O-rings affect the sound? Does it reduce the clack/rattle/reverb (I don’t know the right term/root cause) when the switch “buckles”? Or does it reduce the overall amplitude of sound for the switch?