It's not a defect, but, rather, a time-in-service related Airworthiness Directive. In short, it states that several engines parts must be examined for cracks and fatigue. It applies to just about everything using Tay 6xx series engines, including such primarily civil aircraft as the Gulfstream IV and IV-SP.
I'm *not* an A&P, but I read the AD, and it would appear, based on the parts that need to be inspected, that you'll have to tear down the entire engine to do the inspection.
AA is retiring the F-100's as they hit the TIS requirments for the AD. So, while there will be airplanes parked in the desert, each one will require between 1 and 2 million to bring back into service -- a price which is likely too high for them to ever see service again.
Sad, because I like the F-100's.