I've always used only all castor and have never seen any rust or had to change a bearing. To be honest, I'd never known an engine could rust until I started reading forums like this. Most of my flying, starting over 40 years ago, has been with CL and when I read about the rusting problems in RC I figured the only real difference was the way they shut down after a flight so I've always treated my RC engines the same way...full throttle and take off/pinch the fuel line.