Now listen, I
could be a bit previous here but I ordered these for my 2 Kayfuns...
https://www.fasttech.com/p/1536607
I replaced #16 and #18. No leaks here so far.
The thing to note is when you're tightening the base section together (when it's taken apart), if there's movement/play in the upper deck section then you're not getting a good seal from the o-ring. With these new ones they seem nice and snug and the silicone is soft enough to create a good seal with out making things too tight.
If you don't hear back from me on this consider it job done