Geoff Butcher wrote:Thanks Rich, but my servo is only a couple of years old, it works, and I don't really see how it can cause a problem in the hydraulic system. Now considering the can of petrol/box of matches cure...

I am not sure how the thing works, but I removed my servo and disected it after having problems with a soggy pedal and done everyting first as well. There is no direct link from the brake pedal to the m/c, but this bladder sits in the way and works with air pressure. Maybe it has to do with an airleak, because with installation you need to install a few seals. If it doesn't work the pedal pushes via a rod on the bladder inside but the movement is not tranferred properly to another rod that goes into the m/c.
Anyway it could not work on a turbo engine because of the overpressure in the intake manifold (instead of underpressure) so I removed it and have a direct rod going from the pedal into the m/c. It cured all my braking problems.
Maybe -if you think your servo works- there is a sort of airleak in the servo causing these problems. Perhaps someone who understands the servo better can clarify.