Slightly off topic - Charger brake problems

Yeah, it isn't Mustangs, sorry... had a question though and the technical problems could apply to mustangs, so... please don't ban me

My friends charger has had brake problems for a while. It basically doesn't stop, the brakes do nothing. His front rotors were warped, so we replaced those... didn't solve the problem so we ended up also replacing the spindles and pads, and bleeding the living hell out of it. Didn't help, still. We noticed that the master cylinder, even after bleeding and refilling, would lose brake fluid on both sides (the front brake reservoir and the rear brake reservoir).

We went to a shop and he said the problem was almost assuredly the master cylinder. We noticed that the rear brake line was leaking, but since it is a dual-reservoir master cylinder, that shouldn't impact the front brakes, should it? And since the front brakes do the vast majority of the stopping, we figured that this leak is not the root of our problems. And yes, we will have to fix this ruptured line eventually, but we really just want to get the thing stopping first, so it isn't a priority... unless you think that is somehow whats causing the trouble...

Any thoughts? Is the master cylinder to blame? Are we missing something? The car has power brakes too, by the way.

I believe the point of the dual master cylinder is to seperate the front and rear brake lines... ie if you have a rupture in one line, it doesn't cripple the whole system (so in this case, the rupture in the rear would only disable the rear brakes). In theory I don't think the leak in the rear line should have any effect on the front brakes. Could be wrong though... if anyone could confirm this it'd be nice.

Anyone else have any ideas on what it could be outside the master cylinder?