if u need a cylinder u might as well do the booster also.

i just did mine in my EF and when u get the Cylinder OR the booster it even says in the box "MAY NEED NEW BOOSTER" or "MAY NEED NEW CYLINDER"

Cuz what happens is the seals between the cylinder and the booster goes bad and brake fluid leaks into the booster making both parts no good. air in a hydraulic system is what makes it go straight to the floor.

Replace them both bleed all ur brakes DONT FORGET TO BLEED THE MASTER CYLINDER!!