the most common cause of the wonderfull powdered rust mixed with grease coloured grease on your drive flange isnt the hub side seal failing but the rubber cap becoming porous or cracked...
there is a little bit of fretting thats going to happen to the splines but it gets made significantly worse when you mix it with grease and O2. The fine bits get turned to rust, suspeneded in grease and it makes a great grinding paste.
I've seen countless cases of that on military 110s that get parked up for a couple of weeks then driven around and then sit for an age again. The wheel bearing grease is usually ok but you get a film of cruddy grease with that same color on the outside of the flange.

