@FarsideOfCrazy
I got the seal from here
https://www.aliexpress.com/item/32968937392.html?spm=a2g0s.12269583.0.0.30c545fckoTYLP
The one I got was 6x10 mm but a little wider would provide a better footprint on the kettle bottom, but it is higher so would perhaps hold more wort back.
Not sure...