Symptoms - rear brake pedal has been loseing pressure and stated to go through entire stroke - last few months as bike has sat for a while last night I checked it and it bottoms out completely - no braking at all to rear wheel - tried pumping the pedal...did not increase pressue at all. Pads are fine - fluid is full I assume the caliper seals are bad as the system is air tight and no leaks. If this is this is the case - do I need to replace anything else ie...piston assembly etc... Anyone else had this issue? What else could it be?