Have had almost the same problem with pedal going nearly to the floor. Have done the way home very slowly and put tt in the garage. Next day, I climbed on board and miracle everything was in order. My guess is that the brake sometimes stay to thight and as a result, oil is overheating. That's why the pedal went to the floor. When everything cools down it comes to normal again. The two routes to investgate for safety reasons are: the handbrake cable staying too thight or a stuck brake cylinder.
