The RailCore II was designed around the idea of using linear rails on all the motion stages. It’s important that your rails move smoothly as that motion directly translates into your print quality. There is a video for evaluating rails by Steve White
Various Linear rails have been tested
- Chinese Rails (various sources)
- Genuine Hiwin Rails
- Zyltech Linear Rails
You can rebuild your Chinese linear rails, following the guide here
For lubrication, an oil or grease with a PTFE additive is recommended.