when i got this car i was pissed that some knucklehead had cut the cat out of it. when i first looked under this car i could only see this small crack on the flex disc but since the exhaust had to come down to replace the front pipe (aforementioned head-o-knuckle decided to cut in front of the collector!) i decided to replace both discs.
this is what i found once i removed it from the driveshaft.....
not the same picture!! this unit was almost 75% split
more severe damage....
i think this had less than 1000 miles left on it, if that.....
moral of the story: if you see any cracking AT ALL chances are it is much worse where you cannot see it
edit: i am now glad that i needed to do the exhaust work so i had access to this extremely important maintenance area