Do you guys have a rule of thumb when to change o-rings even when no visible defects are present?
Why ... I guess o-rings can lose elasticity and some other quality without noticeable visual marks that would indicate that, but not 100% sure on what to do.
So, if we assume that t looks good, but is old for let's say 2-3 years ... what to do? In past, with Nikonos this is what I would do exactly ... just to be sure.