Bird, I'm guessing every one of those pressure cookers were a rubber gasket seal, and from time to time required replacement. The All American has no gasket and is a machined faying surface seal.
I'll bet you're right, Al. We did have a big old canning pressure cooker with no gasket, but it was too big to set in a sink to run water on anyway, so we never did that to it. And the others did (and do) have the rubber gasket, so that explains it. Thank you.