Well, I just talked to my neighbor.
He says the jacks do leak a little bit over time, and fixing them is not an option since they are still giving him good service. But his issue is not just how often he has to add fluid, but how hard it is everytime he has to. He says he does check the level with the jacks in the upper position, and that last time he had to add fluid, it took about a quart to refill all of them, and that he usually has to add some more everytime he travels, depending on how often he operates them (he's a winter texan so he basically travels twice a year).
In other words, he wanted me to help him improve something that's not that big of a problem, but maybe could be done anyway. I told him that, from my point of view, it would not be a good idea to have a tank to refill all the tanks using just one line (he was thinking of it the same as the battery watering systems, just use gravity to bring the fluid to the reservoirs in each jack). Doing it that way, there would be no way to control which tank the fluid goes to. And given how the tanks-pumps are assembled, theres no way to bypass the individual tanks so all the pumps would feed off the extra tank. I suggested just installing 4 oil hoses, from the top of each tank to the engine compartment, doing some kind of base, and label each hose, so he could easily add oil remotely with a funnel to the jack that needed it, therefore no more crawling under the moho and spilling a bunch of oil. But then as he said, 'how do I know which jack needs oil? I would still need to get down there to check.' I suggested using some device like a mirror attached to a long stick, so he didn't have to get down there, but he didn't seem to like the idea very much.
Any other options we might be missing?
Thanks everyone for your help. I appreciate it.