He was correct to remove the vacuum hose and look inside. If it was dry, either the leak is very small or very intermittent. You might have to wait until it gets worse so you can find it. Intermittent seals in the master cylinder usually don't stay that way for long. They will leak much worse in a few weeks.
The only reason I suggested the master cylinder is because that's about the only place brake fluid can be lost without leaving a puddle. If it's leaking somewhere else, it should be easily visible given the amount of fluid you've added.
The fluid might be collecting in the power booster. In that case, you might have to unbolt the master cylinder and look at the rear of it to see if it's wet. There also might be some wetness running down from that area on the front of the booster.
Wednesday, October 21st, 2009 AT 2:32 AM