I'm going crazy trying to figure out the brake problem on 85 300sd. I started when pretty much all my calipers started leaking, so I replaced all 4 calipers and hoses. After that I realized the pedal would sink so I assumed I over stroked the master cylinder and got a new ATE one. I bench bled the master, then bled from the fittings on the vehicle, then power bleed a gallon of super dot 4 through all the calipers. Now the pedal will intermittently go very low, in my garage it feels pretty good and firm but if i drive it around sometimes it will go almost down to the floor. I am stumped what to do next since I don't see any hard lines that are leaking and I also replaced the booster a few months ago.