My bet is that when you pull the tranny, you'll find a few sheared sets of threads in the torque converter bosses. If you lose a few of the bolts (which make a godawful racket as they bounce around inside, generally), that can be enough to let the assembly start to vibrate, which can back out the fasteners or even fatigue and shear the remaining fasteners. By the looks of that one hole, the fastener that used to live there had been wiggling in the bore for some time. <img src="/forums/images/graemlins/frown.gif" alt="" />

Pull it apart, you need to check the torque converter and ESPECIALLY the flexplate for cracks... if it vibrated its way apart, there may be collateral damage. Clean everything up really well and look for cracks...

Randii