Where did it go?
Two of the posters in this thread and other links, all whom I would believe, state it takes slightly over 2 quarts, 70 oz, of rear differential gear oil. Why did mine take 4 quarts! then? I don't think I spilled that much.... I do have the back tires on 10 inch ramps, which would cause the back fill hole to be higher and therefore cause it take some more fluid, but twice as much?! The drain pan did have just slightly over 2 quarts which would be the drained oil plus whatever spilled and it caught while I filled the differential. There wasn't much oil on the papers underneath or the driveway. Could the oil have gone up into the drive shaft?
After having lowered the back from the ramps, I suppose I could remove the rubber filler cap and drain any excess that is now over the the level of the filler hole.
The biggest challenge I had with this was getting the new oil in. It just went very slowly. I had to cut a 4 inch vinyl tube piece to push onto the end of the oil bottle spout (though it fell off a few times) so I could move the bottle up above the fill hole. It was still a bit hard to reach in and squeeze the bottle so I found it useful to cut a small vent hole in the top to get rid of the vacuum. The tube end inside the diff needed to be above the fluid level so that the air pressure on the oil did not prevent the oil from flowing into it. Still it took a long time to get the oil into it.