Is it possible that Rives BFK made a black litho paper in the 1980's and 90's? (I believe it was Rives BFK). Prints on this paper have become brittle with time. Has anyone else had this experience? Is there a good archival solution for rescuing this paper?

Works on any paper will deteriorate over time if not protected from the environment and properly framed/mounted. If the prints have substantial value you should reach out to the appraisal departments at either Christie's or Sotheby's as they may be able to assist.