Can't believe I am posting about yet another show stopper. In Spain 6 January (Kings') is a big deal like bigger than Christmas so I take myself off for a tour onto Portugal. At Pomeraõ, a VERY hilly place my rear brake vanishes. Fluid OK, lever goes to a stop on peg hanger. No bubbles in reservoir. Pads don't move. Of course it happened as I came to a stop on a hill so a bit shaken at brake just vanishing. If I pump.the pedal many times (about 20) I get pressure back and it holds for a few minutes. No fluid leakage. I suspect seals in master cylinder but that is just a guess. Bike done 2,500 km from new. I have had it for three months. New but '18 model. So any ideas?