[66sprint6]

My son got called in to work last night, and called me about halfway there saying the brakes were failing. The pedal went right to the floor, and wouldn't pump up no matter what we did. Is this a symptom of a bad MC? The MC makes a gushing sound when I listen when my son pushed the pedal.
I'm also having a hard time finding a replacement MC for a '67 A-body with front discs. I can order with a long lead time, but I'll need one quicker if the old one crapped out. What other cars had the same MC? I'd like to order from Rock Auto and get it expedited if I can.