A little oil is nothing to worry about. Remember, oil spreads a lot so a couple drops is not as bad as how it makes it look. Keep digging into it. Check the actual pad thickness and rotors for grooves

 

You also have to take the entire caliper and mount off to be able to get the rotor and slide out the axles...

Well, either the seal is leaking on it's own...r the bearings are worn and letting the axle wander slightly to cause the seal to leak. This is exactly what happened to my Rack'n'Pinion. My tierod was worn out and wobbling causing my rack to leak out the seal into my boot. Now, I need to change that seal because it's a little worn from the POS tierod that dodge uses.
Also, in NY, you will fail inspection if any oil is leaking from your rear seals as they can coat the emergency brakes and make them not work as intended.
Southern states are much more relax about inspections apparently.

 

Check the E-brakes. Mine fell apart made a good racket. Just a thought.

 

Well after digging into it the top spring for my parking brakes appeared stretched and had come off allowing my shoes to grind against the drum. New spring problem fixed for now until I get around to changing the seal