grease on rim?
 

Anyone know what causes this oil/grease to show up on my rims?
http://i556.photobucket.com/albums/s...511_132455.jpg

Wheel bearing grease?

Looks like wheel bearing grease migrating out from under the dust cap in the end of the hub. JMHO, you may have to seal the cap in place with some gasket sealer. FWIW if the bearings have not been repacked I would do this first but I have whileimatit disease:-)

Brake fluid? I know all the lines start from dead center... But I'd pull the tire and look to see where the. 'Wetness ' begins..

That's wheel bearing grease. Time to check the bearings (they have to get pretty hot to melt the grease enough for it to flow out from under the cap) and repack. Replace the inner seal. Make sure your dust cap is not bent or warped. It may need to be replaced if it's been beat on too many times.