Vacuum piston gasket for Carter BBD two-barrel?

I find a couple of gaskets in the rebuild kits that would fit. The old gasket (#56 in the diagram) usually disintegrates when I pull out the vacuum piston, so it is difficult to determine what a new gasket should look like. The two choices I seem to find in the kits are:
1) a small round, paper thin black gasket, probably some kind of treated paper
2) a small round, cork-looking gasket, a few times thicker than the above paper-like gasket

Anyone know for sure which is the correct gasket? I've been using the thin paper one except for the last rebuild, when I used the little cork one.

One more question, what happens if I use the wrong one? Thank you.

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