There may have been a seal design change over the years. I do know that the early ones with wooden handles have a wide pot rim with a very wide seal. Perhaps the more O-ringish seal with grooves is for later models. Compare your canner with the pdf manual I suggested you download. That manual is a copy of the original National #7. Hopefully some clown didn't mix a top of one model with the bottom of another model...I don't know if that's possible, but who knows!
Call Presto customer service if you still can't figure it out.
That's all I've got. Good Luck!
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