Who aired the 140th episode of the series overall that was the first after the departure of actor Isaac Hayes, after the episode Stan joins Scientology in an attempt to find something "fun and free"?
The Return of Chef:  The 140th episode of the series overall, it first aired on Comedy Central in the United States on March 22, 2006. Trapped in the Closet (South Park):  In the episode, Stan joins Scientology in an attempt to find something "fun and free".
Comedy Central