Boundless doesn't stock these seals apparently?

Yes, I had the same problem with both silicone parts, from both mouthpieces. What I tend to do is place the screen inside the silicone from the other side, and then push the silicone onto the rest of the mouthpiece(the screen is between the silicone and plastic). After a few days, the screen made its way into the plastic part, where I put it from now on after cleaning.

Cool I will try this, many thanks