I had a body man inform me that he has seen numerous late model Mustangs with bad caulking jobs in the trunk area. He checked mine and sure enough. You have to lift up your trunk carpet and panels to see this. Mine was on the right side. It also helps if you shine a trouble light from inside the wheel well pointed toward the trunk. EGAD...lots of gaps and a really crappy job from the factory. These have to be sealed properly or you will get dust and dirt coming in or if you happen to drive in the rain or even wash in that area, you'll get water coming into your trunk and promote rust.