Your M03 will not be complete without one of these. It effectively improve the car performance by at least 1 second per lap. Even though the metal bearing is slightly heavier than the plastic one, the benefits you gain from a more freely rolling car makes this upgrade worth the while. Use the money you save from a discounted kit from RC-Mart for one of these upgrade. You'll not regret it.
One of the first things you should get for your M03! Inexpensive and works great as a first upgrade or as replacement! If you want better performance, remove the internal grease and use a few drops of bearing oil.