I remember seeing rings that size sold for other purposes in sex botiques. Glad you were able to find one in a regular store.
I know from using our glass Cory with the rubber gasket on an electric range that when the water came to a boil, the heat was turned off, the lower bowl removed from the element and then the upper bowl was put in place. After that, the brewer was returned to the surface unit which had plenty of heat to send the water up and finish brewing the coffee. You have to be much more careful of the heat and the steam pressure when using one of the rubberless brewers.
I know from using our glass Cory with the rubber gasket on an electric range that when the water came to a boil, the heat was turned off, the lower bowl removed from the element and then the upper bowl was put in place. After that, the brewer was returned to the surface unit which had plenty of heat to send the water up and finish brewing the coffee. You have to be much more careful of the heat and the steam pressure when using one of the rubberless brewers.