I can see MCAs point, but from an engineering perspective it appears to me that the factor of safety of the stock drive shaft is a bit too close to 1.0. And, again from an engineering standpoint, the cost difference between it and the GT part has got to be minimal.
So once again, we have accountants making engineering decisions. If they can save $10 each on 100,000 cars, that's a million dollars, and that can make some bean-counter's career.
This is the same mistake that Ford made with the Pinto and the lesson has been forgotten.