The problem:

Busted version & the replacement:

How it looks in the sensor shaft seal:

The files are posted on thingiverse.com: https://www.thingiverse.com/thing:6189085
I uploaded the step file to hubs.com and ordered 2 in stainless steal black oxide coated. Two of them cost me $273.25 including tax and shipping. It took approximately one month to arrive. Aluminum would have been significantly cheaper and probably would work just as well.