Only seen it on the rears. Found it the day I drove it home with 39 miles on it. Perhaps the reason its on all fours is that maybe the fronts that have it were once on the rear before the tires were rotated. Im sure the black part of it is brake dust sticking to the grease, because brake dust by itself is not greasy.
I had grease on my front inner wheel. Upon closer inspection, I found that the hub seal was leaking. The dealer took care of the leaking hub seal problem when I brought my car in for the tick and clutch shudder. The tick is now gone but the new clutch also shudders and they put 30 miles on my car probably HOT RODDING it!!!!!
well they had to seat the clutch lining, so you wouldnt have that noxous smell as the lining burned in....kidding. I wonder how these guys really drive these things?