I have a 2006 GP GT SC. When I bought the car the coolant was brown and clumpy, I had them flush it. During the winter it was fine, but lately I've been having to fill up the resivor. I can't figure out where it's leaking. I don't get any puddles under my car and hoses are dry when I check them. I thought for a second about a blown gasket but oil is normal? Why else would my reserve tank keep becoming empty?