The brake fluid contains various small impurities in it, as well as the hydraulic system itself (there's no such thing as perfectly clean) and the brake lines themselves deteriorate.
The reason the brake fluid goes orangey is because of the heat that is transferred during the actual braking. The rotors and pads heat up due to the friction, and heat transfers to the pistons, which in time actually boils the brake fluid. When it boils it changes its chemical composition, turning sludgy and orange. It looks almost as though there's rust inside the system.
I completely replace my brake fluid every second oil change, just to be sure. At $10 a bottle of brake fluid, it's cheap insurance.
And I to my motorcycle parked like the soul of the junkyard. Restored, a bicycle fleshed with power, and tore off. Up Highway 106 continually drunk on the wind in my mouth. Wringing the handlebar for speed, wild to be wreckage forever.
- James Dickey, Cherrylog Road.
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