Up until a few years ago the name of Dr Joseph Yao was always mentioned in connection with Leica in Hong Kong - he is (or was) a noted Leica collector / dealer. However a quick google search suggests that the most recent contact was in 2005 or so, and most the best recommendations date back to around the millenium, so it looks as if he is no longer active.
I do know that he was heavily and directly, personally involved with hospital work during the SARs outbreak in Hong Kong a few years ago - I believe close colleagues of his died through infection in the course of their work. My understanding was that he came through that alright, at least physcally, but perhaps it led to changes in his life. Certainly the SARs outbreak is about the time he stopped being mentioned in Leica circles.