The scoop pictured in image 1 shows the normal wear and tear, and ball tracks, that you would expect on a decade old pinball game. While I normally use a bench polisher for metal ramps and guides, for scoops and other odd shaped pieces of metal a Dremel tool works better. The only other tools you need are a couple of buffing wheels and Ryobi yellow and white buffing compounds (see image 2), which are available at Home Depot. The yellow compound is for removing scratches and the white compound is for polishing.
I usually run my Dremel at about 5,000-7,500 rpm. Since different Dremel models and other brands will vary it's best to go by feel rather than using a specific setting. If the rpm is too low the Dremel will bog down when light pressure is applied and if the rpm is too high the buffing wheel will try to take off on you and the metal will quickly become hot while polishing. Also be advised that too little pressure will also cause the buffing wheel to take off.
Two things to keep in mind, neither more rpm's nor more pressure results in better polishing.
The first step is to clean the scoop thoroughly with a good quality cleaner like ZEP general purpose cleaner. This will remove any grease or dirt that will clog up the buffing wheel or add scratches instead of removing them. Also at this point take note of the original finish on the scoop (check on each side of the ball path). Some metal parts are moderately to highly polished while some manufacturers (like Williams) tend to leave a grain on some metal parts.
Do not use this procedure unless you are looking for a mirrored finish. In the case of our scoop, the ball path is polished while the remainder of the scoop is grained. For the grained areas I use the yellow compound only. Yes I know these areas don't show, but you might as well touch them up while you've got the scoop out of the machine.
After cleaning, fire-up the Dremel and hold it against the yellow compound for 10-20 seconds. Then with a gentle pressure work it up and down the scoop, going with the grain (if any). I usually work a 2-6 square inch area at a time. After a minute or two you can stop polishing, wipe off the compound that is built-up on the scoop (it wipes off easier when still warm) and see how you're proceeding.
You want all scratches removed before you proceed to the white compound. Once you're set, continue the same process using a different buffing wheel and the white compound. Continue as describe above until you've got a nice finish that matches the original finish on the metal. The last step is to use a little Brasso to clean off any remaining polishing compound and add a little more luster. For reference, it took me about seven minutes to buff-out and polish the scoop.
See image 3 for the finished product. It looks better in person since the camera highlights every little scratch that the eye wouldn't otherwise even notice.