I also had the same experience as Wolfman regarding getting replacements for broken motor shafts. I think I broke four or five in the span of two races, and I was told by the Castle CSR that my set up was faulty. I doubt that, since my car ran fine before that for a long time. Anyway, after I raised hell, he reluctantly agreed to replace the motors. I sold all but two of them (keeping them as back ups) and have gone to another brand and have had no issues since. Coincidence? I think NOT.
It is of note that I upgraded all my motors to the "new" design to take advantage of the better bearings that they supposedly have. Instead, I was plagued with a whole slew of motor shafts breaking. If only they offered us an option of getting a 5mm shaft from the factory, I would still be using the Castle motors. This option was also discussed with the Castle CSR's on numerous occasions and I was told that this was not possible. Oh well.