Best treatment for dishwasher rollers that use metal screws
From your picture, it looks like just the washer is rusting. Replace the washers with stainless steel washers to prevent rusting. You can source these from anywhere you can find a stainless washer of the appropriate size.

It appears that the screw and screw-post are not rusting, indicating that they're made out of stainless steel.

Not sure why they would have made the parts out of different materials, but it seems they have - it's probably cheaper this way.