I have a leathered gaff saddle, rtaher than jaws, on my boat. What should I use to lubricate the leather to prevent it chafing the varnished (Epiphanes) mast?
(well, that's what I use - also used on bowsprit traveller leathered ring, shroud lanyards where they go through the deadeyes when setting them up, the bowsprit gammon iron and fid, etc.)
I always use tallow - I bought a tub from a plumbers merchant - brand name Monument (their name appears on a lot of plumbing tools and sundries, so most plumbers will have heard of them).
Tallow's the answer. You can either melt it down and paint it on to the leather, or rub it on when it's solid. Both methods work, which is best I leave for you to decide.