Gokunimbus is right, I had the same issue with the v1 ac9 and multiple RSSTs.
What I did to fix the RSSTs was cut down a carto end cap or I think I even used a piece silicone cap from a old CE2 clearo, I'm sure their are a bugillion different types of e-cig caps that could be used. Basically I just cut down a small piece of rubber or silicon that would snugly fit around the center post and barely fit inside the inner tube (that goes between the atty deck and 510). When I assembled the RSST I placed the MacGyver-esk stop at the top of the inner tube and screwed everything together.
Probably not as clean as replacing the shoulder washer but it did stop the leak.