Try lubing the top cap small o-ring with a very generous amount of VG.
Take the top fill kit off, insert the top cap into the top fill and try turning, rotating, the top cap inside the top fill kit. It should rotate smoothly once lubed up. If it isn't, try replacing the top cap small o-ring with one of the spares.
If it is still too tight consider buying o-rings with a slightly smaller cross section. For example if the top cap o-ring is say 6mm OD x 1.5mm then try a 6mm OD x 1.4mm o-ring.
As far as I can tell, the top cap small O ring doesn't make contact with chimney/juice control piece of the Steam Tuners device. Instead the steel top of the chimney top cap is making contact so there is no rubber to steel contact.
It definitely makes sense that the top cap is removed when you see how the two pieces fit together.
I've been experimenting with more wick and making sure there is none at all protruding from the wicking ports that can catch on to the juice flow as it turns. If there is, the edge of the juice flow control pulls open a window for juice to leak straight into the deck and flood.
I've had a newly wicked build sitting with juice flow full open for the last half hour (chimney top cap removed) and there is no sign of leaking so far. Fingers crossed.
