What happened to brake fluid?

From the time your car left the factory when it was new, moisture from the atmosphere has been entering the brake fluid reservoir from *the vent hole under the reservoir cover. The word hydroscophic means the moisture mixes with the brake fluid. Eventually the moisture will corrode and seize the pistons in the calipers and wheel cylinders. It's cheaper to have the brake fluid pressure flushed to get rid of the moisture than it is to replace calipers, wheel cylinders and brake lines. *Lexus recommends changing the brake fluid every two years regardless of mileage.

I have a few years working on my own cars, so let me fill in the picture.

At one time when servicing the brakes the replacement of wheel cylinders and master cylinders when doing the brakes was common. The idea was to hone the wheel cylinders when possible and rebuild them. This was required because of the way brake fluid changes to being corrosive when it absorbs water.

Brakes lasted about 20,000 miles if they were quality brakes. A person often traded cars about every two years and they cost less then a years pay, often financed for two years.

Today cars are financed for five years and most car owners expect for repair costs to be low. To achieve this car makers have started a maintenance schedule to reduce repair costs. One item which now is supposed be changed on a regular basis is the brake fluid. Doing so increases the life of the calipers and wheel cylinders. Brake pads and shoes now last longer and with changing the fluids often new brake components like brake cylinders last 100000 miles instead of say 25000 miles.

So it is a trade off. Replace the brake fluid and save a couple of hundred on brake parts down the road or do not replace the brake fluid with the result of needing to replace those failed parts that result. 

Cheap Brake fluids are Hydroscopic it absorbs water when Hot

some new expensive Brake fluids claim not to absorb water

Don't Change it at your own Peril Your Car Not Mine

Some car makers made brake cylinders out of aluminum which corrodes when insulted with moisture that accumulates in brake fluid over time. Corroded brake cylinders cannot be repaired and must be replaced. That can be prevented by flushing brake fluid every few years to remove any water.

It has always been a good idea to flush the brake fluid. I recommend every 40k miles to my customers and charge 50 bucks including fluid - big frickin deal, just do it but don't pay $200.

Over the decades it got better.

Use DOT 5 brake fluid if you don't want to hear all the hype. 

Pay some MONEY for good brake fluid!  You want the best brake fluid for the lowest cost, no doubt. 

Just flush your glycol based DOT 3 or DOT 4 brake fluid every 2 years.

Nothing changed with brake fluid. People never do preventive maintenance on their vehicles now just like back in your parents day. I wouldn't recommend flushing the brake fluid until you need a master cylinder or calipers for no other reason then bleeder screws can snap off and then you have to replace calipers.

It's a question of prevention, not cure, so you DON'T suffer the "catastrophic failure" you seem to want. 

It is indeed hygroscopic, which means it absorbs water.  This water can not only give rise to corrosion, as already mentioned, but can also boil from the heat within braking systems.  This gives rise to gas bubbles in the fluid, which are compressible, and can lead to brake failure. Personally I'd rather change the fluid than find out too late that I should have . . .  

It's not difficult to do, just takes some time.  What you're doing effectively is bleeding all the brakes thoroughly until all the old fluid has been expelled and new fluid replaces it.

READ the owner's manual and follow the recommended brake fluid change.  Do not OVERTHINK it.  The ENGINEERS who tested your car already did the overthinking.

Expensive ABS pumps happened. I still question the need to flush more often than every 100,000 miles though.