You make good points. Lord knows I do not want to swap out the rear end. I am sure it would be a day of finger smashing and angry cussing. I have been guilty more than once of not doing the simple stuff first, so am going slow.
This diff was never dry,though it may have been a tad low when I started. Adding oil certainly did not quiet it any.
I raised the car again and disconnected the drive shaft at the diff;
No play or leak in pinion. Drive shaft has good u-joints with zerk fittings.
Reconnected drive shaft, put in gear and listened with stethoscope;
Noise at pinion, noise on both inner and outer bearings, really loud noise at diff. cover. I suspect diff.wear, but I guess I need to listen to my good 240 to compare noise as I dont know what noise is normal.

I am aware that differentials in general are overbuilt, and many howl, yet will function for thousands, or tens of thousands of miles, but I still make long trips in the wagon and do not want to be stranded, or fear being stranded.