The issue you are having seems to be more and more common. There is another recent thread on the forum dealing with the same issue. I had this issue last year and am experiencing it again this year. Soft pedal. Long travel to the near or at the floor. No leaks. Full reservoir. I even had my fluid changed last year and it's doing it again this year (after sitting for long periods its worse). I had the dash light come on and go off as well. Brake pads and rotors are fine.
I'm taking mine in on Friday to have a shop that specializes in german cars look at it. I'll let you know what I find out. Please do the same if you find out sooner.
Update? Has anyone had to replace their master cylinder? (kstewart; brake fluid should be changed/bled at factory specified intervals).