Please note that the terminology: "Cruise-O-Matic", describes several different transmission units in the Ford production line.
Although often similar in design, each unit was engineered for it's unique application.
For example, I believe the 352 FE engine of this period generally received the "MX" version or "medium size" units of the C.O.M. transmission; but, the 430 MEL's received the "Lincoln Multi-Drive" or sometimes referred to as "Lincoln" or "Large-Case" units , only titled as the C.O.M. in T-Bird applications as they are Fords not Lincolns.
Generally, I believe the noted failure of these C.O.M.s was/is the development of cracks in the rear bulkhead of the cast iron gear case. This lead(s) to loss of hydraulic pressure and function failure. The practice of abruptly shifting from the drive position to reverse or vis-a-versa, particularly with the wheels in motion (poor driving technique) is generally attributed to the cause of this failure. This failure seems to be less prevalent in the "Large-Case" units. I don't know if this actually results in the tailshaft flying off, but that event does happen for a number of other reasons, and not unique to C.O.M.s.