Die Marquise Von Sade (1976)

aka: The 1000 Shades Of Doriana Gray

A lonely aristocrat Miss Gray (Lina Romay) has a twin sister who is in an asylum. They share a strange bond. Miss Gray is rational but frigid while her sister is insane yet feels sexual pleasure for both of them. A female reporter (Monica Swinn) arrives at the mansion to investigate. Also stars Raymond Hardy, Peggy Markoff and Martine Stedil.

Comes from a German widescreen import print.