wheel sensor problem

My friend has a 2013 double cab 4x4. His 4 hi/4low, ABS and traction control lights all started flashing, and he can't get it to go in 4x4 with them flashing. We pulled codes, it says the problem is right rear wheel sensor circuit, we pulled the right rear sensor and it had oil or grease on it, no visible oil leak on the brake system. The left rear sensor was dry. We replaced both sensors and the rear harness, individually, still flashed, so we cleaned the sensors and connections and put the old parts back on, cleared the code, and it came back on within 20 miles. Is there possibly a problem with an axle seal leaking oil onto the sensor? Do you need to clear the codes and drive a while after changing a part? My 2010 did the same thing at 36k miles, ended up being a broken wire in front of the rear connector, took dealer 3 days to find it.