On the military axle there are two threaded in fittings per wheel bearing. one is a plug and the other is a spring loaded vent or grease purge. I am going to add a zirk to replace the plug, but I am debating on the vent fitting. From what i read it lets grease out and nothing in, but at its age can i trust it? It isnt rusted, but i am worried about letting water into the rear bearings. Have you guys just left the vented one alone or have you replaced it? tHanks!