There is a reason those PPC connectors DO NOT have a o-ring or "washer" in them. Notice any connector of quality doesn't have them, because they can cause the ground to float, raising the potential for issues later such as lightning strikes, equipment damage, and the dreaded pixelization and tiling.
A proper port seal covers the base of the port and extends up onto the seal area of the connector (and NO the spark plug boot is not a proper port seal). It thereby seals all the threads and the port area from moisture migration. Your spending .25 or more to make a connector that is worth less than .05, it freely allows moisture to penetrate the thread area causing corrosion and decreased grounding, later the butyl rubber your "seal" is made of will break down due to ozone and it will leak like a sieve. With power being freely passed thru the system electrolysis only accelerates the damage.
PPC, SNS, Gilbert, Digiconn, Holland, Stirling, and anyone worth their salt will tell you the same story, O-ring in the nut = non SCTE approved = not in my system