The "end of life" spec is .5VDC, you should change antifreeze before this ....I recommend .4 to my customers, most say a tad lower than that.
Google up antifreeze voltage test....here... »www.completeradiators.com/articles/34.htm It's not an uncommon way to test at all and is easily the single most accurate way to do so.
Now as for there being any sort of lubricant in antifreeze ?!? Exactly what is getting "lubed" ? The sealed waterpump bearings ? If the antifreeze ever gets near the waterpump bearings the pump is toast and should be replaced (you will be able to verify this by looking at the antifreeze spewing from the waterpump weep hole). Nice try.
Lubricant is a bit old-school, I'll give you that. The newer deal now is anti-corrosion additives, for example those present in Dexcool (OAT) if you're driving a GM vehicle. Those absolutely *are* depleted over time.
