In the video, the green thing is the gasket. It should be reusable, but nothing's guaranteed in the world of waterproofing.
I really like the look of the Pixel watch 4's approach to this:
https://www.ifixit.com/News/113620/the-pixel-watch-4-is-the-...
I really like the look of the Pixel watch 4's approach to this:
https://www.ifixit.com/News/113620/the-pixel-watch-4-is-the-...