This is my first Harley. I just went over 6000 miles. I called the dealership where the first owner had it and said that they changed the oil at 1000 miles with the Screaming Eagle 20w-50 oil. When changing the oil the owners manual tells you to remove the hose at the bottom and drain it completely. It also says that you don´t have to drain the crank case. WHY? Wouldn´t dirty oil remain the crack case. Also, I am thinking of changing to AMSOIL 20w-50. Has anyone else used Amsoil and is there much difference?