well guys, i've been out of the 'stang" thing for over a year, but I'm about to buy back my 99 GT Steeda. The car has been barely used in the past year and has developed an oil leak from the rear differential. 2 years before it's "sitting in the driveway" period of its current owner I had Ford install 3:73 gears, and never had a problem. In inspecting the car yesterday it was obvious the diff is leaking, can see oil spotting in driveway and in the underside of the gas tank. I drove the car yesterday and it felt/sounded ok, is this a major concern? or a simple gasket failure?