This seems like a great subject for its own thread - one that might attract 645 users (I'd be happy to chime in there).
On the subject of professionally used RB67s, I would point out three things in their favour:
1) they are built like tanks to start with;
2) many were used exclusively in the studio, and were therefore not exposed to the elements and other hand-holding dangers;
3) the RB67 system is designed to be repairable; and
4) as the RB67 is highly modular, and generally different versions of the component parts are compatible with older and newer versions, so it is relatively easy to replace just the portion of the system that is worn out, while continuing to use the rest.