So if the brake fluid in our master cylinders and resevoirs is SEALED how does the fluid get contaminated by moisture?
Is the culprit condensation?
Is the 24 month window pretty much rule of thumb for brake fluid flush and refill / line and banjo fitting inspection ?
Not to split hairs too much, but it's Hy
groscopic, not Hy
droscopic.
hy·gro·scop·ic
/ˌhīɡrəˈskäpik/
adjective
(of a substance) tending to absorb moisture from the air.
@Gert - Nicely answered Sir.
The secondary impact of not changing your brake fluid every couple of years or more often is the potential to have a ring of corrosion occur around the brake caliper pistons. This is especially prone to bikes that sit over the winter, or longer. The problem becomes evident when you go for a ride, apply the brakes and the piston doesn't retract due to the corrosion. Shortly your brake rotors start to glow from the heat generated by the dragging pads and you end up with expensive repairs.
On ABS bikes this can occur for the solenoid piston inside the ABS block. That gets really expensive! $4k for a repair like that recently on my wife's GSA due to the dealership charging for service they didn't do. We paid them for flush/bleed of the brakes, they didn't do it. Didn't realize it until the ABS failed, caliper dragged and it ended up being ABS block, rear rotor, pads and a plastic guard that melted. Aftermarket extended warranty replaced it. The wife lets me service her bike now instead of relying on the dealer.
Detailed service records would be helpful to someone in the US that had an extended warranty and was making a claim. I've had bikes with well over 100k miles that still were under factory extended warranty. One claim, (CCT), the Mothership asked for receipts for my owner service. The dealer scanned the pages in my owner's manual with my service log, where I had added lines going well past where the original ones left off, and detailed everything done, and the tire log I had kept on the bike since new. The Mothership took one look and never asked for receipts again. The dealer told me about this after the fact, and laughed at the response he got from the Regional rep about it later.

They aren't used to people that actually ride their bikes and maintain them.