Tim, if this is the Castello we spoke about last weekend, my guess is that all you may need to do is open the tenon to around 3 - 4mm, and then with needle files work the button end to open the air passage. If you insert a regular pipe cleaner from each end, you will be able to get a feel for the exact location the tightness begins and ends. You should only need to open it enough for a cleaner to pass through easily, it does not need to be opened wide right from the get go. Start in small increments, until it feels right for you. You can't replace the material once removed.
Regards
Michael J. Glukler
Regards
Michael J. Glukler
