My Brother has a 98 Chevy Malibu he wants to sell but the power steering foams the oil and quits working in the winter, works fine in the summer. We checked the usual leak points on the oil cooler lines and they have been repaired and there is no signs of leakage anywhere. It has to be sucking air from somewhere but there's no leaks, we were thinking of throwing a power steering pump at it next week but I don't like to through parts at something I don't understand. Any ideas, all I can find on the Internet for any search is ignition switch recalls.