Came across this great interview from the A.V. Club with G.W. Bailey, who played St. Eligius's psychiatrist, Dr. Hugh Beale, a good ole boy from Mississippi, on the first season of St. Elsewhere. He left the show after one season, and this interview explains why. Turns out he didn't get along with executive producer Bruce Paltrow. After leaving St. Elsewhere, he landed his iconic role as Captain Harris in the Police Academy movies. He currently stars on the TNT series, The Closer.
The experience he relates may shed some light on some of the other cast turnovers of the show's six seasons.