M_Boats: M15 trailer jack

I frequently sail in salt water (SF Bay) and am having trouble with my trailer jack seizing after a season or two. I religiously rinse it after each sail, but I have the impression that rinsing is ineffectual; the sea will always win. I disassembled it and poured penetrating oil on the screw and block and finally freed it; now, what is the best way to clean and preserve the threads. The outer assembly is galvanized, but I can't tell about the threads on the screw, which are covered in grease and rust. Is Navel Jelly the answer, or are there better products on the market? I know Fulton now sell a salt water jack, but I have two of the older models and would rather not buy a third. Thanks, Bob Becker 1982 M15 #208 SF area