86 420sel Brake/engine Questions

[82LANDYACHT]

I have an 86 420sel and I have some brake problems. I replaced all 4 calipers and bled the system a couple of times but the brakes still fell mushy. When you get into the car the brakes feel fine but as soon as you start the motor the pedal goes almost to the floor. Also, it has a click coming from what I think is the left cylinder head. I pulled the valve cover and everything looked ok. Lastly, I have an oil leak coming from somewhere in the back of the motor. It only leaks when I run the car and comes out of the two holes on the bottom of the engine through which I think I can see the fly wheel. Any advice would be appreciated. Thanks.