Why is there air hissing out of the brake pushrod?

What is your question?

The brakes are spongy but no pressure goes to the floor and air is hissing out of rod that enters some kind of cone thing connected to the brake pedal. Replaced the abs pump ( not the problem. Replaced the cylinder on the drum brake for drivers side rear. Then bled the brakes. Still not the problem.... not sure if it is the booster the master cylinder, looks brand new. Dont want to keep dumping money into it? Would it be a bad booster or master cylinder?

What makes this problem better or worse?

Nothing

How long has your 2010 Chevrolet HHR had this problem?

4weeks