Good question, to which I haven't really found a workable answer.

All of my seacocks are Marelon and the tag on the valve handle recommends
lubrication (I think) every six month.

I haven't figured out, away to do this with the boat in the water..

With the old bronze seacocks, there was a drain plug where you could install
a grease zerk.. Nothing like that on these..

This is not to say that I'm not happy with my Marelon valves. I operate them
frequently (some several times a day, when I use the head) and although the
seam stiff, they still work smoothly..

And no disimilar metals problems to worry about. )))

As far as the type of lubricate, I would have to check the recommendations
on one of those paper tags. Later

Steve
s/v Good Intentions