Engine Roar 2007 S550
first of all, what exactly was malfunctioning on your ABC system?
Regarding your description I'm 95% sure that the pulsation damper / shock absorber (black bulgy thing, sitting on your ABC hydraulic pump) needs to be replaced.
It's this thing right here:
http://www.bk-fahrzeugteile.de/shop/...0004660010.gif
hope this helps.
Regards



