What makes an o2 sensor tick is inside, and I've never seen a way to actually clean them. They have a life expectancy of 80, 100,000 miles, after that they are recommended for replacement. By removing the soot you may have increased the flow through the parts that do the work.
An O2 sensor is actually a little electrical generator, it's amazing they last as long as they do given the enviroment they have to work in.
The insides consist of ceramic zirconia and platinum, oxygen reacts with these mediums to create a small electrical charge, the computer uses this charge to determine if the car is running rich or lean, more oxygen, more voltage, less oxygen, less voltage.
Retreat? Hell, we just got here......