When i went for inspection a month ago ,subaru dealer told me ,i have head gasket leak and he told me he added a little anti freeze to the car,but i didnt see any leackage in my parking lot i park the same spot all the time,since he told me i keep checking the level its the same normal level,even since he told me that i drove my car 500 miles,i opened the oil cup i didnt see any white stuff, i checked the oil its clean,i didnt see any white smoke in the exhaust only in the cold weather in the morning like any other cars do for like a minute,and they told me the repair cost is 1550 dollars, and the car doesnt over heat,its normal temp gauge,i am confuse can you give me advise