I recently got a 2005 mustang v6 from a used car dealership. The car only has 66k miles on it body looks good interior is great. The check engine light came on an hour off the lot so I ran some test. Nothing seemed to show up but the 4th cylinder misfiring. I also see oil leaking out of the cylinder. (When I am idling, pulling away from a stop or reversing the car shakes pretty bad). Could this be a valve stem seal issue? Any advice would be greatly appreciated don’t know much about cars yet this is my first one. Thanks