Yes you're right all the technical papers that I've found show equilibrium for the most common Nylons i.e. Nylon 6, Nylon 66 and Nylon 610 at 50%/60% humidity. The equilibrium is achieved after more than 100 days There is no information when the humidity is frequently over 80% plus exposure to salt water, as it is in La Rochelle where the boat has spent a lot of time and where it's moored today with the humidity at 88%. The figure appears to be more than 5% water take-up but, and this is the most annoying part that, it continues to swell with a unit that has previously been machined.
The fact is that swelling has happened repeatedly showing that it is a continuing process. The swelling must stretch the material and it does not appear to recover original dimensions on drying then swelling again later.
HDPE and moulded PTFE are contenders and maybe use the old fashion solution of Lignum Vitae. Some tangible cooperation from Opacmare would be helpful. They haven't even advised which Nylon they use and clearly not considered at all an alternative.
All this bother with a product that cost the price of a good small car when new!