Most plastic and metal electro-mechanical scoring reels can be cleaned using
soap and warm water, CP-100, Wildcat #125 playfield cleaner, or Novus #2.
I prefer using Novus because it works completely, quickly, and leaves a
glossy finish. So far I haven't found anything that doesn't come off with
Novus. If you don't have this you may find that some soiling may require
two of the other cleaners to be removed. Be cautious when using the more
powerful solvents such as CP-100 or Wildcat. It is rare, but some Bally
score reels have been known to lose ink with too vigorous application of
these solvents. This is another reason why I prefer Novus.
For a single-player machine it may be easiest to remove the reels. For
multiple-player machines it is easier to clean them in the machine. Be
careful when cleaning them in the machine that you hold the reel still while
you rub, otherwise you may damage the mechanism.
Note that paper reels cannot be effectively cleaned.