From Unofficial Zero Manual
- General Brake Maintenance
- Check for pad wear or debris.
- Keep the pads and discs clean.
- An occasional brushing of the disc holes is worth doing maybe once a year.
- Check hydraulic fluid level.
- Make sure the brake fluid is in good shape and the type/specs you need.
- If in doubt, replace with fresh fluid (not from an already opened bottle).
- Make sure the brake fluid reservoir is not over-filled (top).
- There has to be some empty space, or your bike will be lightly "braked" and your disk/pads will deteriorate prematurely...and you will get less range.