I have a custom power steering/hydoboost system. Uses a GM type 2 pump and a remote reservoir. The hydroboost kept foaming the the fluid and the pump would start to whine. Bleed the thing for hours and still could not stop the foaming. Old timer told me to put in some Dexron. Figured I had nothing to lose so put in about a third of a cup and foaming stopped! No more pump whine and everything feels better.