Great advice. I have two part clusters here and one is super clean such as you see in the photo. The other one is pretty dirty looking...like dirty grease. I guess it depends what environment the cruiser was exposed to.
Here is a better photo. It seems like a part that could be swapped out from another cluster because it is just a dial that feeds off the main odometer that resets itself to zero whenever the driver wishes.
I found one photo on my work computer but I can take more when I get home. This is generally what it looks like behind the speedometer face. When you push the long black button(which is hard to see in this specific photo)...it lifts off the gears from the trip odometer and resets it.