Second that thought. 9 out o ften times the accumulator has taken a squat. Probably wouldn't be a bad idea to flush the brake fluid while you're at it.
gnttype.org has a good write-up on replacing the accumulator ball. If I recall, you need to pump the brake pedal 10 times, place a rag where the accumulator screws into the PM, unscrew it, screw in the new one and your done.
That's pretty much it, be SURE you de-pressurixe the system (pump the pedal at least 10-12-times). From there just screw the old one out (maybe a 3/4 wrench??) and screw the new one in..