thrust washers do not wear because there supposed to turn on the shaft with the propeller.So ,either the prop is defective or someone really wailed on the prop nut
bending the thrust washer.
I physically put the washer back on the shaft and there is no way it could reach anything that it could rub up against, but now that I think about it, the anode that gets mounted just forward of the washer was so deteriorated that it was loose and probably what did the erosion.