well,,, did you happen to touch the wheel when you were pulling it?
get into the habit of giving each wheel hub a little love pat everytime you stop. this way if its getting warm you will know right away.
that could cause thin grease, and the stains you mention.
could be caused by bad bearings,,,or even improper greasing
seals could be bad, clean it off and watch to see if it does it again.
jack it up and see if the wheels spin properly...or do you have to use two hands to turn it? bearing could be over tightened by a sasquatch wearing mechanics overalls.
or it could just be some neanderthal was just too hammer happy and bent the little silver cap so bad it leaks
all on its own. this would be aggravated by the same cave dwelling knuckle dragging oaf pumping so much grease into it that back preasure squirted it out.
of course any pergerative or otherwise less then flattering pronouns i may have used apply only to profesional mechanics.