Not according to Nissan. Take a look at the FSMs again. I don't have time to sift through each one, so I'll use the '72, '78, and '81 as examples. Page GI-10 of the '72 FSM clearly states, "approximate refill capacities" in big, bold letters. Not any single transmission, engine and differential are going to be exactly the same. The 240Z is lacking in information however, and not just in this section. They assume you will fill to the plug. Page MT-5 of the '78 FSM does state to fill up to the plug hole. The '74 and up FSMs all state to fill to the fill plug, they never tell you to fill exactly "X" number of quarts, and the 240Z shares the same differential as other S30s and S130s, therefore, you should fill then all to the fill plug (notice I don't say until overflow). This is also clearly demonstarted in two photos (trans and diff) on page MA-25 of the '81 FSM. End of story. This is simple logic, folks. Gearboxes are designed to have a certain oil level in them, not an exact volume. Approximate fill capacities should only be used to make a decision on how much oil to buy. You can do whatever you want to your car, but if your procedure is incorrect according to the manufacturer and the recommendation is given out publicly (like an internet forum) then it must be corrected. Don't take it personally, you can do as you wish. I'm not telling you what to do, just informing everyone of what should be done by design. Unless maybe you know something that the engineers don't and have a good reason to change the procedure...