Dan
When you get some washers you may want to set up a little test stand. Drill a 5mm hole in a piece of metal and clamp it in a vice so you can get to both sides. Assemble a wheel with new washers and bolt it to the plate like it would be on the machine then see if it turns smoothly and if there is no axial movement. If all is well put that wheel back on the machine and test the next. etc
good luck
Dave