I think my first step would be to contact the PO and ask why they swapped out the OEM for the plastic job? Was the OEM a poor performer, damaged is some way or? Must be a reason. You could then contact Michigan Wheel via their website or call them for technical assistance in ordering a new prop. We used a plastic 4-blade prop on an outboard many years ago for a performance improvement at a cheaper cost that aluminum or SS. Like Ken suggested, I had everything on board including the OEM prop as a backup in case the plastic prop was damaged.