Clean o2 sensors?
#2
I've used a cloth to clean deposits off the outer shielding, but I'm not sure about any liquid solvents. The only thing I can recall about using liquid solvents is dont bc it can damage the sensor.
#4
Most people will tell you it's not worth the trouble. If all you are cleaning is the steel outside shell, you aren't accomplishing much. The sensor/sensors itself are deep inside and not really easily reached. Most chemicals will destroy it also. Some people have luck by heating the sensor with a propane torch until it turns a dull red to burn off contaminents, but most say just replace them and move on. Sensors generally fail because the heating element goes bad, there is no fix or cleaner that will help with that.