Alfa spider s3 brakes

[Geoffscars]

I own a 1986 Alfa spider s3
2 litre twin dellortos bell and colville conversion

I was driving it the other day when the brake pedal went to the floor. There was a bit of braking but not much. Pumping the pedal helped

I thought it was the master cylinder but this is about 5 years old and when I took it off and examined it there were no leaks
I have checked all the callipers flexible hoses and pipes plus it wasn't and isn't loosing fluid

There seemed to be a stain of fluid around the pipe which runs from the engine to the servo but again nothing inside or anything obvious

Any ideas of what to do next