Thanks GLLHG and Simon for those reassuring comments. I feared something untoward was going on.
I met another owner at Cliveden today and he had the same experience. I will change my garaging habits. I have decided to stop doing that anyway and on wash days I will stop throwing the last rinse water through the hubs.
I also wondered if Switching the engine off while heavily depressing the foot brake, which is what I do, semi locks the servo Pressure on??? does that sound feasable?