My primary fuel filter banjo bolt only takes one of the orings too. Not sure where the other one goes unless its for the prefilter (doesnt fit tho). The plastic seal at the top of the filter is necessary and should have come with the new filter. They are loose so it may have fallen off somewhere.

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Treetops
06 E320 CDI 127K Miles
87 300TD 231K Miles

99 E300 269K Miles-Sold