94 civic hatc. cx. stock.
whenever my car is at a dead stop on a downwards or upwards slope the brake pedal slowly sinks to the floor. i bleed it once because when i first bought the car it was sinking whenever i'm at a dead stop, i got some bubbles out and now only sinks at slopes. could my master cylinder be gone?

 

Sounds like the seals in the master cylinder need replaced. Or you have aleak in your brake booster. But the most typical problem is the MC.