E-TON Viper 90R Owner's Manual page 93

TIP
Some maintenance items need more frequent service if you are riding in unusually wet, dusty,
sandy or muddy areas, or at full-throttle.
Hydraulic brake service
Regularly check and, if necessary, correct the brake fluid level.
Every two years replace the brake master cylinder and caliper, and change the brake fluid.
Replace the brake hoses every four years and if cracked or damaged.
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