If your brake pedal goes to the floor and your pedal assembly is full of brake fluid, it's time for a new brake master cylinder. Here's where we get all Zen on you and do you a big favor:
Unless this is a "concours d'elegance" thing, do your self a favor and page down to the 19mm master cylinder. This is a slight upgrade in our opinion. With brakes we tend to shy away from the word "upgrade" as it gets bandied about a bit too much by the sheisters out there but, a 19mm will give you a slightly firmer pedal which we think is a plus. It will (laws of physics) take slightly more effort but, trust us, you'll get use to that in a few minutes. Better pedal feel and, the best is yet to come... LOWER PRICE.
Final note of Zen do good: We're not fans of the Chinese import master cylinders out there as of yet. They'll go by names like URO and Hamburg-Technic (slick). There's been too many failures for us to recommend or sell them. If they're charging over $75 for that stuff, you're getting ripped off. If it's less than our prices, it's probably not ATE.
Our stance today: Use original ATE master cylinders. The others may have better QC in the future but for now... brakes are an important part of your "staying alive" plan.