A year ago, I cleaned out all the bearings in solvent, removed ALL old grease, and repacked with Red Line CV-2 synthetic grease. The bearings have 300k miles, give or take.
My car has taken to whining at highway speed, and the whining reduces a lot when I turn a certain direction. It really sounds like it's coming from the back, so I pulled the bearings for a looksy. Both sides rolled free with the car in the air. Left side bearings looked great, here is the right.
Outer bearing (smaller)
The roller surface has a gray stripe in the middle, but the grease looks completely healthy. It looks tan because it was shot under HPS lights. The inner race looks OK.
Inner bearing (larger)
The roller surface seems ok, the outer race looks fine, but the grease looks filthy and muddy. Again, brand new grease. It's all over the bearing like the bearing is causing it, but could it be something else like water ingress from a failing lip seal? What's wrong with it?
The spindle looks great, with no obvious slipping.
I have spares of everything. Which ones if any need to be replaced?
Edit: It turns out I was looking at the wrong side. On the left side, I found the nut much looser than I had set it. It had a muddy inner bearing (from an ancient lip seal leaking; replaced) and a weirdly dirty outer bearing. (my grease is Red Line, literally red, so I can instantly spot dirty grease). I dunked the inner bearing in solvent for cleaning, fished it out with my finger and repacked it. Dunked the outer bearing, fished it out with my finger, repacked it. Put it on, it was weirdly grindey with inner bearing installed. .
So I got another bearing from a junkyard pull, test fitted it and it ran smooth as glass. I dunked it in the same solvent, and fished it out with a screwdriver this time. The screwdriver came back covered in metal shavings. I could not believe so much metal shavings could come out of one bearing. Wait. Did this metal come from the original bearing or the junkyard pull? Then I cleaned the solvent, re-dunked the junkyard bearing until no more metal shavings appeared. Repacked it, put it on the car, smooth as glass.
Now I've re-solvent-washed the original outer bearing, a little more metal shaving showed up (a-ha!!!!) Clean/dry/in my bare hands it runs VERY lumpy with a little pressure. It didn't look all that bad on the rollers and races.
So I think that was my problem. Yay, I'm about to do a 3000 mile cruise!