Trevor,
Personally, I would be really cautious about using stainless under water or any where without contact with oxygen (ie buried in wood) especially if galvanic action comes into play – as I am sure you are aware Stainless & aluminium are poles apart galvanic wise. I have had personal experience (on a previous boat) to this effect – stainless looks ok on the outside but in the wrong circumstances crystallises & weakens internally. This is the main reason why I went for aluminium again on my pintle (though as with stainless you need to consider the grade you need for the job in hand). It’s also why I have taken steps to isolate the stainless from aluminium – at least a visual inspection of aluminium or steel etc tells you when its time to get a new one.
Regards,
Simon