Bad rear axle seal? Nasty wheel sensor:

Hey guys,
I had the code read for my ABS and Brake warning lights on the dash, and it came up with the right rear wheel speed sensor.
I pulled it out, and it had a notch chewed into it, and it was covered with this nasty greasy dark fluid.
I continued to pull out the left rear to compare it, and it had a little bit of a lighter milky/healthy looking fluid on it, and it was not chewed up at all.
Could it be a blown axle seal on the passenger rear? How common is this? And could that be the reason why the sensor is chewed?
What do you guys think?
Thanks!

 

Post pictures.

Sensor is after the seal, there shouldn't be any fluid of any kind in there, possibly grease.

How many miles? Check your wheel bearings for play, usually that's the first sign you're losing a bearing (leaking that is). Check for fluid inside the wheel.

 

This^^^

There shouldn't be any fluid in that hub assembly and if it looks milky it is contaminated with water.

All of that aside what chewed a groove in the sensor face? The only thing I can think of is the bearings coming apart in that hub assembly...

 

I'll lift it tonight and check for play in the bearings. I thought it was weird that there was fluid also, but I thought that since the fluid looked really clean that it was almost somewhat purposeful in there. It didn't look bad at all.
I couldn't figure out why there was a chunk out of the sensor either, though. It looks like it has been going on over lots of time though. The only thing I could think of happening to chew a notch in it is if all of the grease got sort of gritty in there over time, and slowly built up on the spinning part inside and over time it sort of ground it down the sensor until it couldn't sense anymore. The driver sensor looks brand new, though. It is just weird.
Maybe I need to just pull both of the rear assemblies apart and check out what I've got going on and find the culprit.
I'll pull both of the sensors out tonight and take pictures as well so you guys can see what I'm talking about.
Thanks!