In the 80's an older retired guy told my friend that he must use USED motor oil to oil down his auto body to prevent rust. Some of us contend that our car's useful auto life ends before the engine quits means that extending engine life is to no avail. Use that old motor oil and prevent rust. I wonder if that used motor oil had thinned out so much that it could get in the nooks and crannies. He said you had to use used! Anyone else know about this?