I have had a Duopar Eco since the early 80's. I am not much of a bicycle
technician but I don't recall any problems installing it. I have just
transferred it to my new/old Mercian. It is still the best shifting rear
derailleur I have ever owned. I still have the plastic bit that tended to
fall out.
Lawrence Bradley, Tacoma, WA (but of the Kentish Diaspora)