[wevoid]

Regardless of opinion surrounding whether aftermarket couplers cause transmission wear, there is one fact that is not covered here - so far.

The stock coupler has only one true plane of rotational freedom - perpendicular to the axis of the pin - it is rotational freedom that allows for misalignment.
The slots in the factory bushes allow a certain degree of rotational freedom (again for misalignment) in another plane at 90°, giving a crude but adequate universal joint. The slots are essential to allow the misalignment freedom on the second plane - the lost motion fore and aft is a legacy of the slotted bush design.

Stock couplers with round hole bushes eliminate the second plane of freedom and for certain could lead to accelerated wear in a number of places in the shift mechanism and transmission. A stock coupler with round hole bushes requires that the shifter be arranged exactly on the same axis as the main shift rod of the transmission if the system is to exist without a "forced position".

As mentioned by Shaun, the factory arrangement allows for all parts to be slightly misaligned - a condition almost certain to exist in all cars.
A true unviversal joint will accommodate this misalignment in a more pure way than the stock coupler.

As for the vibration, I suspect most of it originates in the transmission and Porsche were attempting to isolate the vibrations from the shifter (and driver), not the reverse.

Regards

Hayden