I've polished those coin reject buttons to a chrome-like shine on a buffing wheel with green compound. The hinge, if the discoloration is the nickel or zinc plating flaked off and bare metal showing, you're never gonna get an even shine on that unless you replate it. On the cast pot metal coindoor plate, the difference in color shows uneven chrome plating, but that should just be on the inside where you don't see it anyway.