That seal isn’t available. The cork seal was intact in this gear case but was no longer tight around the prop shaft. I just made, and added, a leather seal on top of the cork one. Here is a link with some tips on how I make gaskets. https://youtu.be/I0FrFA__n00?si=ON_CXt34_b2EvVql
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.