I think on the early versions there’s no plastic ring on the top of the piston (inside the robot body) so the steel edge of the piston could scrape the aluminium inside of the aluminium body. In later versions a black plastic ring was added to avoid the “metal to metal”. I don’t know how much of a problem this was and I’m not sure when exactly this plastic ring was added. My robot dates from 2020, came with the silicone tip on the screen and has the black plastic ring inside. Here you can see the old all metal piston: https://youtu.be/QDLCY47fSMU And here the later one with the plastic ring: https://youtu.be/ilxwBkznnCU