It’s always a treat to hear from Brazil, Andre! There are probably some streaks of old glue in the gasket tray such as shown in that last photo. I don’t think there is any reason to remove them. The white gasket strips probably will break up somewhat and crumble when you start removing them. The residue should be able to be scraped off using edge of a knife blade. In my experience, that does not have to be done perfectly. Be sure there’s nothing loose remaining; wiping with alcohol will clean it well enough so that the adhesive backing of the new gasket strips will produce a seal.
I am very interested to hear how this works out for you. The Pianica 32A is one of the best vintage Yamaha or Tokai Gakki models (the earliest models were designed by Tokai Gakki and released under both names). It’s a good instrument.