I bought my first Boss302/GT500 part for this Mustang. The 2013 GT500/Boss302 differential cover. It has the cooling fins to help keep the rear diff cooler. I had this one drilled and tapped for drain and fill plugs and to relocate the rear axle vent. The stock fill plug is located on the front of the diff and is hard to get to. This will make changing the differential fluid easier. Also, if I ever needed a rear differential cooler, I can easily hook one up.