In Auto Motor Klassiek you can regularly read that it is absolutely necessary to change the brake fluid at least once every two years.
Tip one: use freshly purchased brake fluid and not the can that you have already opened thirty years ago, because that brake fluid has been able to attract moisture in all those years. Tip two: when venting, always start with the brake point furthest away from the brake pump; make a circle until you end up at the nipple closest to the pump ...