Do I need to replace vacuum booster?

[jammy]

Hi:

Re: 1999 Grand Prix 3.8L

Here's what's happening:

• Brake pedal goes to the floor, no resistance at all
• No leaks under car
• Reservoir was empty; filled it, pumped pedal and level dropped, but still no visible leaks.

From what I have read, this is most likely an issue with the master cylinder seal, and fluid disappearing without leaks means that the fluid is leaking into the vacuum booster.

Question: Does this mean I will have to also replace the booster when I put in the new master cyl?

Thanks!