I've got an old tractor that has been tucked away with 4-5 year old diesel fuel in the tank. When I pulled her out briefly last summer, she smoked hard and was drastically down on power. Obviously the fuel has gone stale. Rather than drain the old fuel (it is a large tank), is there anything that could be added to it that would bring the fuel back to life? I realize that the horse is probably out of the barn on this one, but its worth a shot. Thanks in advance.