To answer a few questions raised, when in service they were charged with dry compressed air. At the Workshops, we had a static compressor and they regularly charged up a supply of small cylinders, so that we could charge the accumulators in Saracen, Saladin and Leylands, of which there were a lot about in that period. Some other equipment came into use in later years that used nitrogen (oxygen free grade). I have used that gas to charge Saracen, Saladin and Routemasters during the course of my business. My recollection is on Alvis MV's, the pressures were to be checked every 6 months, the seals are not very efficient and a ram type seal would have been better, I knew an engineer who owned a Saracen and he got a hydraulic company to make a new piston with a proper modern type seal in it. Charging pressure is 500 psi + or - 50 psi. for the Saracens and Routemaster so would assume it is the same on Leyland.