I actually have one of these watches as well, given to me as an 18th birthday present by my parents. It still works but unfortunately it didn’t take me long to get the face scratched and chipped, which is something that now pricks my conscience each time I look at it.
Every now and then I enter ‘Casio S21’ into eBay and/or Google in search of one with a better condition case. If you still have yours, please let me know if you’d consider selling it