If you pressed the brake pedal all the way to the floor, that will often take out the master cylinder due to running the lip seals over the crud that builds up in the lower halves of the bores where they don't normally travel. Now it's a matter of getting the air out.
Before we get to that though, leaking brake fluid has nothing to do with the parking brake. The parking brake is totally mechanical; no brake fluid involved. It is more likely you lost a rear wheel cylinder. GM had a real poor design that used a wheel cylinder that was held to the backing plate with a metal ring with two clips. The hole in the backing plate rusts out or wears away, then the wheel cylinder can rotate. The pistons pop out, you lose the brake fluid, and the shoes are no longer in adjustment so the parking brake cable won't apply them either. That said, it is possible for the parking brake to still work if no other parts fell out of place.
Look inside the two rear tires for wetness indicating the need for a new backing plate. The redesigned plate uses a regular wheel cylinder that's held on with two bolts, not those silly clips. You'll want to take the old wheel cylinder apart to read the diameter on the inside of one of the rubber lip seals so you buy the right diameter replacement. Don't leave that to chance. There are going to be four or five optional sizes and using one even 1/16" wrong can lead to a brake pull.
Wednesday, March 2nd, 2016 AT 6:24 PM