Spongey brakes on 2000 LeSabre

I have a 2000 LeSabre with 32,000 miles. Brakes have been spongey for a while, Buick dealer said they were OK. Today I had master cylinder and front brakes replaced. Still spongey. Car stops OK, but with constant pressure on brake pedal, you can the feel the pedal sinking ALMOST to the floor. My other 2000 LeSabre has much more positive pedal fell. Gets stiff about 1 1/2 inches down and has a little of the sinking pedal but not nearly as much. Any thoughts?

Thanks,
Jimmy

It sounds like you have air in your lines or a bad brake line.