Another article in favor of replacing the 02 sensors:
http://www.obdii.com/articles/Replac...intenance.html
Don't know that I would go with the Bosch recommeded interval at the bottom but, I think at 100K plus it's not a bad idea. Don't use the less expensive types you have to splice the connector on. These sensors are sensitive. If it's not spliced exactly right it could give you problems sooner or later.