The 62 Jaguar was leaking fluid from the rear differential at a decent rate. Especially after a long run when the gear oil would get nice and warm.
I suspected, and still do, that the culprit was the drain plug.
So, with unknown oil in the diff, I set about draining and then filling it with new oil.
I choose valvoline 80/90 as it is ok'd for hypoid style gears, exactly the type of gears that the MK2 puts the power to the ground with.
It was not a bad job. Except for being careful not to strip the male-end soft-metal drain plugs. I used a new crescent wrench to get them off. When replacing I used a thread sealant, this has helped me stop pesky oil leaks in the past.
The filling is always a bit messy, but a 6-inch length of clear house made it a bit easier to get the fluid in.
How'd it work? Don't know. It is too hot in Denver to be driving that thing. Like wearing a wool suit with a leather vest is how it feels on summer days.
And, if anyone can explain why gear oil stinks like burnt hair mixed with old french fry oil, I would love to hear it.