Queue99
The M100 is the same as the Japanese version of the U100SX, so the VSC3 can be installed.
I believe the M100 is a first generation silent, so the key sensor board is corroded.
I've been experiencing this symptom a lot lately.(U5AS、U30AS、U300S、U100SX,U300SX,etc)
Parts were no longer in supply.
I guess vintage synthesizer repairman may be able to fix it.
I guess RSH3 is better than VSC3, the reason is that the old silent mechanism is also replaced and the touch when silent is better.