When assembled correctly, no shafts in the purple Dispenser should fail, regardless of how much use it sees. A recent Game Manual Update included an addition to Appendix A, which explains this situation in further detail:
The arm can jam if either the standoff above the ratchet pawl or the pawls on the end of the arms are placed incorrectly. Checking your build against steps 30-31 and 36-37 of the VIQC Slapshot Build Instructions might help identify the problem.
The plastic shaft was designed as an intended failure point to protect other parts of the dispenser that are not as noticeable. A steel shaft will not fail as intended, and unseen damage can lead to intermittent issues such as the Dispenser skipping or taking more rotations to dispense.
For this reason, intentionally assembling the purple Dispenser with a metal shaft for the ratchet gear is not an acceptable solution, as it may cause further unseen damage later on.
If an Event Partner finds themselves in a situation where they are at an event with a failed plastic shaft, and do not have any other plastic shafts available to replace it with, then a metal shaft would be an acceptable temporary replacement if and only if care has been taken to ensure that the underlying assembly has been fixed.