The used car salesmen was a pratt, he clearly thought it was the newer synthetic brake fluid.I was shopping for a new car (used) for my daughter yesterday. The brake fluid on one was very dark. I asked the salesman when it was last changed. He was adamant you no longer need to EVER change brake fluid on the new breed of cars. He opened the cap, dipped his finger in and wiped it on the car's white paintwork, to show me how clean the fluid was. He confirmed it was DOT4... We walked away.
Nevertheless, either way, master cylinder rubber plunger will not last indefinitely . . . . . .