Have you noticed even the genuine dizzys wear the top bush? Which isn't a bush, just runs in the alloy housing which gives lateral play at the top? There is no lubrication for the top bush at all... This would upset the gear mesh in some form or other...

Cheers,
Tim

all dizzies have been bushed like that from the 1950's. usually a cast iron or sintered bronze bush.
the aftermarket dizzies have a brass bush which doesnt wear but instead wears the chinese steel shaft
but due to the length of the dizzy shaft, and the fact that it is also located into the block, means the 1 or 2 thou wear you get on the top does not make much difference to the gear mesh at all.
The top bush gets lubricated via oil running up the shaft, while the engine is running.

like i said 99% the failures youve heard about are related to an aftermarket distributor gear. you wont have the issue with the factory gear no matter how much wear is in the top bush.