The left front hub on my '99.5 F250 is leaking lubricant that has sprayed all over the outside face of the wheel. I figured it was grease squeezing out of a deteriorated bearing in the hub, so I started to disassemble and got down to a bare hub (rotor off).

The hub turns freely and there is no noticeable play in the hub.

The leaking lubricant looks and smells like differential lubricant, but I don't see how diff lube could get to the outside of the hub. My hub seal appears to be weeping a little at the end of the axle housing inboard of the axle U-joint, but I figure that's 'cause I've got a problem with the axle shaft seal in the diff housing.

I have a new hub to install, so I'll go ahead and do that since they have 180K on them. But has anyone seen this before and can you explain to me how what appears to be front diff lube could migrate to the hub assembly?