So I recently purchased my first BMW not off to a great start. After I test drove it I noticed a small leak I told the dealer who then replaced it the valve cover gasket cover and assured me that was the cause. Not noticing anymore leaking I purchased it. That day I started to hear a very loud hissing noise only from inside and when driving. But it stops when I brake or even touch the brake. Also I noticed its leaking again. Whenever I park I take a peak under and there's always 4-5 drops on the driver side. And also I don't know if its just the fuel gauge but I just filled up with premium and my gauge is down almost 1/4 after 38 miles. Anyone having the same hissing noise or have a solution. Any ideas of what's leaking and could that cause poor mpg?