I have managed to fix these sort of issues by using a fine metal polishing compound and paper towel (I use Autosol compound in tubes - awesome stuff...) Once the copper surfaces are bright, give them a buff up with a fresh piece of paper towel to remove any remaining compound. The bulb bayonets can be given a light buff up with very fine steel wool (0000 grade). You can swap them for T10 LED wedge bulbs to really brighten up the cluster and you can get them uber cheap on ebay in bags of 10. They are polarity sensitive so you have to install them all the same way.