Pedal spring snapped? This will leave brake pedal approx where it should be, but resting on the rod/ M/C rather than being held from it by the spring.
Brakes work fine then nothing then peddle hard then there fine again If it ever stops.raining I will get the spanners out
When they go hard, try lifting the pedal. If you can lift it the spring is bust or the shaft the deal is mounted on is seized. This has to be dismantled to lubricate. It can be a bit of a faff so may never have been done.
It could be the diaphragm starting to fail... I've seen this on another vehicle... Also check the hoses and the one way valve at the back
