Ok. Sorry. I read where you said "positive pole washer" and sorta fixated on that not realizing you were talking about the entire positive pole assembly (post holder, insulator, washer, and screw). I used my Erlk with the standard pole holder both with and without the black AFC adjuster, then switched to the open pole holder without AFC, then put the AFC back on. The open draw pole holder without AFC is a slightly (very slightly) more open draw (think 2mm air hole) then the standard pole holder without AFC (1.8 mm air hole). Putting the AFC back on the open pole holder in wide open position makes it about the same as the standard pole holder without AFC. In all configurations I needed the positive pole washer to make contact on my ProVari.
I think what you are calling the washer is what I'm thinking of as the spacer/insulator. The taller, tan part in your link. Maybe? I don't think that's going to have any effect on a leak. I'm relatively certain that any leaking is going to be coming out of the top (notched part) of the 510 piece,
the ground terminal.
To be completely honest, I've never really understood how that part that you linked to works. I've been under the impression that the air flows through the notches on the ground terminal (that I linked above) and the two little notches cut out of the underside of
the base then into the holes cut into
the positive pole holder. Being that that spacer/insulator is located well below the holes on the positive pole holder I've never been able to figure out what difference it makes. Hopefully someone more knowledgeable then I can help here.
As far as leaking goes, I've never really had an issue unless my wicking was not done correctly, in any configuration.
EDIT: Actually, as I look at the part you linked I guess I do understand. It's not round and won't block air coming up through the bottom of the positive holder. As I recall you're also supposed to turn the ground terminal 90 degrees so the notches don't line up with the notches cut in the underside of the base. Effectively blocking air flow at that point, and allowing air to flow through the entire length of the positive pole holder. I think if you're looking at this as a method to resolve a leaking issue, the only thing that's going to happen is that it will leak out of the bottom of the positive pole holder rather then at the top of the ground terminal.
Also... what DreamWithin said (since it was much more succinct and better worded).