I have a 2012 Legacy with the 3.6L engine that has started losing engine coolant. Not much, but a little every few days. I don't believe it is a head gasket issue, as I have been through that before. My mechanic says it needs a new engine oil cooler and there is a small leak at the base of it. Before I lay out about $300 for the part, I want to make sure he is right. Anyone here have any input?