Question about c-50

[Promod]

I have two of the C50 maxx motors. Ran them as a dual set-up until the one motor broke the shaft. Than ran the other motor as a single. It lasted about three packs before that motors shaft broke.
The shaft on these motors must be WEAK as there were a good number of people who broke shafts on these motors. A 5mm shaft would be a wise choice.
Thank you,
Promod