:: Bad
Casio replyed saying there is nothing to do. As it was 80's, there is no more replacement parts.
:: Good
I drawn the rubber switch!
I put the image in the same folder I put the photos (it is the first):
I also included the specification of rubber switches from others Casio Keyboards.
Next step is to try a CTK/WK rubber switch, as it don't appear to be so different from the CZ-1's.
Att,