Pedal will always go lower the first push. That'* the whole reason for the saying "Pump them up" The pedal is higher with each pump, pretty much.

when the master brake cylnider went out on my parenst car the pedal went straight to the floor. Good thing it went that day not the day before we had about 1 ton of bricks ye old dodge ram. That think would have never stopped I bet you have leaky wheel clydiner.

All the master cylinders I've ever had go went straight to the floor. Leaky lines will give you that slow continual pedal drop unless the line is totally gone.