Hello, I have a 2003 Discovery with 135K. I notice a pretty good coolant leak during the winter when the heat is in use. There is no leak at all during the summer. My AC has not worked for two seasons so I don't turn it on. A local garage did a pressure test and said there was a leak in the head gasket. If it were just the head gasket wouldn't it leak all year long? I'm willing to bet there is a slight leak in the head gasket but think there may be more going on here. Any thoughts? Thank you for your time!