Interesting topic. I got my local garage to replace the seals in everything bar the MC, also flushed out with new fluid. Previously firm pedal thereafter had a little bit of travel, but worked well, easily stopping from 100mph. Just 100 miles on from rebuild, I left the house noting that pedal seemed to go a little further before biting, drove 5 miles, had to do emergency stop only to find virtually nothing there, ...off into hedge. Tyre marks on road showed only two wheels barely locking. Extracted car (little damage) drove home with pedal seeming fine. Left car sitting for two weeks, got in again to find pedal went straaight to the floor. No signs of leaks or loss of fluid. Must be the MC