Q: what is the distributor o ring, and rear main seal on 1995 Honda Civic

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on estimate it says "Distributor cap leaking rear main seal. I couldn't find those parts in the description section
(1) Answer
The distributor o ring is described here
The rear main seal is at the rear of the engine , where the crankshaft couples to the transmission.
Incidentally a badly leaking distributor o ring can appear to be a leaking rear main seal since the distributor is located directly above the rear main seal.