How to un-seize 02 sensor?
Heat the bung that the sensor screws into enough to remove the sensor without getting it red hot. A big wrench helps too.
Try a mixture of 30% acetone (nail polish remover) and vegetable oil. Keep it capped when not in use so the acetone doesn't evaporate. https://www.engineeringforchange.org/news/2012/08/14/how_to_make _penetrating_oil.html
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