When I removed my distributor (63 valiant, slant six), I only found one O-ring, the large one that fits in the block recess. I read somewhere that there are supposed t be two O-rings. True? If so, where does the second one go?

Two; see here

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Where does that second o-ring go? I do see a smaller one already in place on the dist shaft. Is that the one?

Locations are described in linked post: small/lower in distributor shank groove; large/upper just under hold-down plate.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.