I know that it is a good idea to change brake fluid every few years but hadn't appreciated quite how old fluid can deteriorate over time until I opened a front brake master cylinder/reservoir today. I had already removed quite a bit of coagulated nasty gunk before I thought to take a couple of photos. Yuck
they recon brake fluid draws moisture but the black colour could be the seal slightly breaking down john
It does & is the main reason to replace the brake fluid, it the water content is high it can boil & have brake failure, once cooled the brakes come back. Reason for unexplained brake failures years ago but brake fluid has also improved over the years as well.