Mighty Mouse no longer mighty

It would appear that my Mighty Mouse has decided to take the Mighty out of it’s functions. The roller ball will no longer scroll down! Everything else works fine with the thing, scrolling up and sideways. The buttons still function and it looks in good order, I can only guess it has jammed up with fluff or something. Yet can you clean it? Hell no, there does not appear to be any way of opening the thing up to blast the crud out. At least with the old roller ball PS2 mice on the pc you could take the screw out the bottom and have some fun. If any one knows of a way of fixing this please let me know, single button mice are now really painful!