I think I have finally reached the point where the screws are now tight enough and the phenolic washers are sealing as they are supposed to. After the last tightening there has been no further leak. I think soaking the washers in gas for a day or so before install is the thing to do. I know that you have to be careful about cracking phenolic washers so I didn't honk on them initially. I think the washers have absorbed gas and softened a bit which is why I have needed to tighten the screws to get to this point.
