The answer to how did the
oil get everywhere is simple. The wind blew it while you were driving. I have found
oil as far back as on the driveline in some of my cars when I had a major leak at either the intake rear gasket or a valve cover gasket. A little
oil with the wind can look like a lot more than it is. That still sounds like a lot of oil for a rear main unless the whole darn seal fell out.
Ron