[hammersmith]

I had the exact same problem till yesterday. About 2 weeks before I parked it last year l replace my front passenger side wheel seal and it was all good no problem for a week then I would have to pump twice to stop sometime's not always though.Blead the brakes multiple times but the brakes would never go soft in the garage only when I moved and then not always. Put on my new tires Friday so I pulled all the drums off just to have a look and there it was a broken pin and spring on the back brakes. Never thought of the back figured it was something to do with my work up front.l have the same set up as you with no braking assistance so it's a pretty simple system it baffled me. Got a spring kit for all four wheels pads where all good so I freed up the adjusters and no more problem .l hope you're problem is as easy