[Mr V]

I'd suggest steel too, your transmission shaft is a mission critical part that can't be easily changed between matches so I vote for overkill. Back in Breakaway we had a similar failure though in that case the snap ring groove wasn't even needed for our end application. It happened to us the night before ship date and twisting at other components meant I had to get the sawzall out to fully disassemble and we were blessed by the fact that due to the heavy snows on the east coast that season the withholding allowance was increased. We shipped our robot with a lot of things missing and had a lot of fun at the event putting it together with the new steel shafts that did not have snap ring grooves.