The Porsche 928 S4 and GTS with automatic transmission suffer from a serious problem. The clamp that holds the drive shaft firmly attached to the flexplate (and thus to the crank) is not up to it, and slowly lets go of the shaft. The shaft creeps out of the sleeve and positions itself further to the rear. This causes a permanent pressure on the flexplate and on the crank. There should be zero or minimal pressure on the flexplate. The thrustbearing of the crank can handle pressure to some degree, but if there is more pressure it wears out very quickly and causes massive damage to the engine. This will result in a total loss of the engine.
Some say you should release the pressure regularly. But many do not do this and it is a very temporary solution, so the problem builts up from the moment you drive the car again.
There is one proper solution: replace the flimsy clamp with a decent one that holds the shaft firmly and prevents slipping. It is a DIY job, no need to remove transmission or so. It can be done in two hours.
This new clamp is made of steel, coated to prevent corrosion, consists of 3 lobes that perfectly match the flexplate coupler sleeve. It uses 3x M12 high strength 12.9 Hex key bolts to torque down the clamp to 120Nm. With this new clamp the problem disappears completely. It holds the drive shaft just like the Porsche engineers specified.