I was able to answer some of my own questions about the Mavic derailleurs by looking through some old catalogs last night. They were still available through about 1989, by then grouped with the "star-fish" crankset. The model designation was 851, replaced by the indexing 860 in 1990. The Mavic Timeline indicates that Mavic started building "easily disassembled" derailleurs in 1978. Was this the same derailleur, or were there several versions? I seem to recall an earlier version, but still thought it was later that 78/9. Was the same basic unit really available for 11 years?
Wayne Bingham
Falls Church VA