Air in brake system
Ok, my brakes are driving me nuts. I got this car (86 Honda Accord dx) and the pedal was soft and the light comes on. I thought it was a faulty MC, since it went to the floor. I replaced MC (Yes I bench bled) and bled the entire system twice. I am still getting an air sound when I push the brakes and it travels to the floor. It stops the car, but slow and late.

I inspected the calipers: no cracking in rubber.

Inspected the rear wheel cylinders: no leaking or cracking.

Inspected all four rubbers hoses that attach to the calipers/wheel cylinders: They are hard and a maybe a little brittle, but no cracks.

Back right bleeder screw will not bleed out. Only dribble.

When I bleed the back left brake I constantly get air, so I assume that may be where my problem is. I got under the car but it seems that the line goes up into the frame? Do I need to take the back seat out to inspect the steel line?

Any thought would be greatly appreciated.