I’ve always had a problem with the brake pedal, on my Plus Four Auto, put your foot on the brake pedal to start and the pedal is high, as soon as it starts it drops just over 2”. The factory have tried a new master cylinder and booster, but to no avail, also the booster pushrod on some may not have any threadlocker on them. So the heat is not a problem for me.
That's interesting, there is a sequence of tests for a servo that exhibits the symptom of long travel on the second press, would have to look it up, but IIRC you test the difference between engine off vs on, as it could be a vacuum fault
