This company has been around for a few years. It's a one man operation.
The company DOES make a C-30 gasket. Click on the "gaskets" link to see them.
I have bought several from this guy. The first one lasted about a year before it started to melt down and disintegrate.
The second lasted about 6 months and the last one didn't even fit the C-30 Coffeemaster properly. I then gave up and went with a Cory all glass vacuum pot. Same great coffee flavor as the Sunbeam without all the cleanup and filter mess.
The replacement seals are made from some kind of rubberized silicone. They are strong. And the originals I had fit perfectly and make a perfect seal. But there is no internal spring.
One thing about this guy is that if something is not right with your seal he will replace it for you with another without charging for the replacement or shipping cost. So I guess that counts for something.