while they do fail, I would start looking at your vacuum reserve first.
see if you have a leak somewhere else.

put a vacuum pump on the booster and see if it holds vacuum and the brakes get better.

a bad master doesn't fail like that normally.
pedal to the floor for a bad master, or slowly falling when holding the brakes.

hard pedal is lack of vacuum or bad booster.

they also make the electric vacuum pumps to help too. you could hide that and thus still look stock.