A common issue with (mostly) '85 and up "automatic" 928's is the flex plate clamp migration forward...which if left unchecked, can result in thrust bearing failure...which in the case of the 928 engine, results in catastrophic engine failure.
There are several aftermarket pieces to help stop or reduce this issue. Do your research as to which one you think best fits your needs.
I chose the Ritech Systems unit because in didn't require the torque tube to be removed...and it seemed to be the only unit that totally stopped any forward movement of the clamp.
Here is their photo of the unit:
How my clamp looked prior to loosening...note the spline area showing.
How it looked after releasing tension...note the [reduced] spline area.
I went ahead and marked the clamp position with red paint...for future reference.
Here is the Ritech clamp installed. (Although not required, I still put some blue Loctite on the nuts/bolts)
Again, I marked the front and back with red paint, for future reference of position.