If you haven't bought one already, you might want to just try to find a roller on ebay or something. In fact, it's too bad that I saw this thread so late. I sold my T4 roller two days ago for $50 with tons of extra parts. I just got tired of breaking it and that's what happens when you go as fast as you can with a MM system on 3S lipo.

The real downside to getting the RTR version is that you are paying for a motor, esc, and radio that you aren't going to use.