This is one of those R/C areas that is full of strange incarnations, potions and practices, it gets almost as strange as some of battery practices. Many of these are frankly unwarranted practices that have not been justified with any attention to the facts. With RC motors there are two things that do need to be broken in. The first is the brush to armature interface, and the second is the bushings assuming you have a bushing based motor. Brush Break-in The first part of a motor to break in is the brush/commutator interface. As the commutator is not a replaceable part we want to extended is life as much as possible. To do this you want to make the brushes conform to the shape of the commutator but in so doing generate minimal wear on the commutator. For standard 05s first adjust the timing to zero and then run on 2 to 4 cells for a short time period until the full brush face is conformed to the comm. This may take just a few seconds with serrated brushes to five minutes or more with some hard brushes. Don't use comm drops during this time as they act as a lubricant and will extend the break-in period, not what we want to do. There are special break-in drops available, but these seem to have been developed to get more money from your pocket.  I run the motor on two cells on 12 or less turn motors or on four cells for greater than 12 turns. Run the motor until the serrations are fully seated, do not go to long here, 5 mins max. I use a motor stand to help get this done.
Once the motor is in the boat the load of the boat on the motor will cause high current to flow through the brushes, any remaining high portions making contact quickly heat up and quickly wear away exposing fresh brush material behind it. Don't forget to reset the timing before running the motor. Water Dipping Do not water dip an 05 car motor with removable brushes as this will wear the brushes away far to rapidly. Water dipping is pretty much reserved for sealed endbell motors (those with non replaceable brushes) since the manufacturer will use very hard brushes in those motors (to provide long life). If you don't dip them it will take a long time for them to break-in and achieve the full performance potential of the motor.  The dipping method involves dipping a motor in a jar filled with water. The fluid around the armature causes a high load to be placed on the motor, and high amps to flow, plus it provides a mild abrasive action which causes the brushes to seat quickly. Run the motor on 4 a cell pack for a few minutes or until you see the water start to change color from the brushes wearing. I know you might be thinking water and electronics don't mix. Water is an insulator and although we are not dealing with pure water, the water we use has a very high resistance. The real problem with using water is corrosion, so make sure you thoroughly dry the motor when you are done. You can use WD-40 which displaces water, then lube the bushings.
Bushing Break In Breaking in bushings is something that should only be done on bushing equipped motors. Whether or not the bushings need break-in is determined by spinning the motor with the brushes removed. The resistance to turning (friction) is a good indicator of how tight the bushings are. If you can't remove the brushes it will be very difficult to tell unless you have another broken in motor or have been doing this for some time. Bushing break-in is accomplished by putting a little valve grinding compound into the bushing and spinning the motor. If you don't have any grinding compound Brasso is an excellent substitute. This will wear the bushings thereby freeing up the fit between them and the motor shaft. The compound should be applied using a carrier (like motor cleaner) to allow the compound to penetrate into the area where it will do its job. The process will start out slowly and will rapidly accelerate so be sure to check the fit frequently. Compound in the bushing / shaft interface may make it appear as the bushing and shaft have not worn as much as they really have, so thoroughly clean the bushing to confirm the amount of play. The motor should be turned by a slave motor throughout this process to preserve the finish on the commutator. If you can remove the brushes on the break-in motor during this process. Make sure all the grinding compound is removed from the bushings prior to putting the motor into service, or short bushing life will be the result. | 
