I've narrowed my selection to this list, sorted from most expensive to least. They are all available locally at either NAPA or AUTOZONE, and both have free shipping over $35 (in case a store isn't close to you).
All of these can be used in either limited slip (locking) differentials or not, except for the $19.29 LIQUI MOLY, which is for open diffs (like we have) only. That means except for LM22090 they all have special additives for locking diffs added.
Right now I'm leaning towards LM22090 because it's "specialized", if you will, for open differentials. I'll get under the car in the next few days and get a feeling for how much room I have to maneuver a liter bottle of fluid to the fill-hole. If it's super-tight then I can be convinced that going with a squeezable pouch might be in order. And yes, I watched the funny ad in the post above! I would have been convinced to contact my local "Amsoil is my side-thing" 'dude', but Valvoline (also in a squeezable pouch) scored number 2 (was the runner-up to Amsoil) in the Amsoil "face-off". Like one poster commented, "At half the price you might have just sold a lot of Valvoline!"

$21.49 https://www.autozone.com/greases-and...art/854795_0_0
$19.29 https://www.napaonline.com/en/p/AICLM22090 GL4/5 (NOT for locking diffs)
$18.99 https://www.napaonline.com/en/p/AICLM2048 GL5 (multipurpose gear oil)
$13.99 https://www.autozone.com/greases-and...art/977482_0_0 (squeezable pouch)
$13.19 https://www.autozone.com/greases-and...1-quart/1437_0