A very interesting read...I'd post the text here, but it is a scanned document that won't allow cut and paste of text. On pages 2 (last para) and 3, he cites Article III of the first section of the Constitution to illustrate that SCOTUS Judges are NOT appointed for life.
You're right. They serve on "good behaviour". They can be removed (not likely) or pressure can be brought to bear to force resignation, a la Abe Fortas.