I have a 1998 Ford Windstar, that suddenly started making an annoying high-pitched squealing, constant, that increases with acceleration, and decreases with decelleration. Idler pulley, tensioner pulley, and serpentine belt were replaced. After a 5-minute test drive, the high-pitched squeal returned. The belt was removed, and there was slight wear on the outside edge. There was play on the power steering pump pulley (in and out on the shaft) Power steering fluid was a dark black in color and thin.
In your opinion, would replacing the power steering pump be the next step?