Actually looks like you never had any GREASE in the birfields, just gear oil.
I got the front diff fill plug off and it took about a pint of gear oil, which suggests a leak since it was changed about 23k miles ago, but I can't be sure it was filled properly since I had never checked it.
I pumped some grease into the inspection ports, did the dipstick again so they both look good.
I pulled the front axle breather, not easy to find, doesn't seem to show up on parts diagrams. It's on the back side of the axle, driver side, maybe 18 inches away from the fill hole. I blasted it with some Brakeclean, couldn't really tell how plugged up it might have been, but it's completely clear now. It didn't look like something that needed to be replaced.
So I don't have any scientific results yet but I'm greatly comforted to know that I'm good on both gear oil and grease, for now. I'm going to clean up the driver side, really clean it up, spray it with some foot powder and see if I can determine exactly where the leak is coming from and how much. I'll try to remember to report back when I know more. Thanks for all the help.