You are replacing #6 right?
I don't know about the 92-95 Civics, but 96-00 Civics came with different distributors even on the same year and trim. Maybe a previous owner changed the distributor and the o-ring is slightly off? Just an idea.
Are you sure its coming from the o-ring? The honda service manual asks you to put some hondabond or RTV sealant near where the distributor goes into the head. I would make sure to get a new valve cover gasket and apply the sealant to the areas described in the service manual.