Years ago, I briefly tried to find the saturation limit for brake fluid. Online, couldn't find it. I asked a mechanic I knew... he had never run across a hard number. So its obscure information. Point is this: anything hygroscopic [which brake fluid is] at some point finds a saturation point and moisture starts falling out of suspension. Droplets, now separated, will collect - a low point vs a light fluid. So if a caliper is the low point, the maintenance is really important. Some systems may route a hose or tube on the lower control arm then back up to the caliper which helps buy some time on old fluid maybe, but not much.
The way a lot of oil change places "flush" brake fluid is a scam plain and simple. Unless they are pushing all the old fluid out through the bleeders they aren't flushing anything. Most places suction out the old fluid from the master, top off with new and call it flushed...scam!
It could be anything. Cap seals on brake booster allowing moisture to come in. Brake bleaders doing same. Basically any where there is a bad joint or connection. Brake fluid draws moisture in. As bad as what he showed you should fix issue and flush entire system
The brake reservoir cap is not sealed. As the brake pads and shoes wear down more fluid fills the brake calipers and wheel cylinders. This fluid is coming out of the reservoir, so atmospheric air must displace the fluid. It works against the braking system to have a pressurized or vacuumed reservoir. Atmospheric air that displaces the fluid in the reservoir contains moisture. Car manufacturers typically call for brake fluid replacement or flushes every 2 years regardless of mileage.
Pete is correct. Like changing oil at the proper intervals, brake fluid should be flushed as well, don't wait till it looks dark. I do mine every 20, 000 miles even it it looks decent in the master because I can't see inside lines and calipers. Cheap insurance to keep the system operating as new.
It’s mainly a scam. This only needs to be flushed like every 50-75k miles but places will recommend every 30k. This whole industry is a joke. What’s the risk if you never flush it out? The risk is prolly $500 worth of lines and a single flush is $200. You do the math
