Seizing Seacocks? Try This.
Some seacocks, especially older ones, have a 3/8-metal plug in their bases, typically with a NPT thread. A time-saving, maintenance-encouraging move is to remove the plug and replace it with a 3/8-inch "Zerk" fitting, either of the straight type or with a 45-degree bend, depending upon what works best.
Next time you notice a bit of stiffness in a seacock’s valve mechanicals, simply shoot a little grease inside via the Zerk. Make sure to use grease that’s compatible with the mechanicals, by the way. Some units have rubber inserts that will dissolve in regular grease so you should use silicone-based waterproof grease instead.
Some of the older-model seacocks have a threaded metal plug at the base and in order to pump grease into the device, you have to remove the plug and temporarily replace it with a Zerk fitting that's compatible with your grease gun. But hey, why do this sort of thing again and again? Why not leave the Zerc in permanently? And for that matter, why not remove the plugs on all of your seacocks—if they are of the old-fashioned type—and substitute Zercs. Next time you need to grease one seacock because it's getting a little sticky, it's fairly easy (or easier than it used to be) to grease 'em all.