Although I use and like the Contax 645 I was curious about your post. Are you considering it? It may be a 'dead' system, but there are three important facts: there is a lot of "New " stock around as well as many used, secondly there is repair by Kyocera for 10 years (and many repair shops can do simple CLA, I understand) and lastly, they rarely break.
As you can read here, pros that use it are staying with it, some are buing it now, The latest Phase One cP65+ comes in this mount, as does many new items like the leaf and Hartblei.
The lenses are great, REALLY great, and the system's one small weakness is in slower AF than some of the latest Hassrey, Mamyia and now Leica-but not by much.
In the end, it is built and behaves like the Mercedes of cameras, and has Zeiss designed and QA/QC lenses.
Prices are fair. If I were evaluating a new MF system, I would actually consider it again.
But I don't have to-I have it and use it as my main camera system (Oh and the Hasselblad V lenses work well, even with focus confirm.!)
regards
Victor