I went through this in May.. always had a leak at the rear of the engine since day 1. I did two rear mains in the garage while the engine was installed (not fun). I finally gave in and took it to a shop, they also diagnosed it as a rear main seal and they replaced it.. it did not leak until the next day when there was a small puddle, which got gradually larger. I just gave up, and figured I would be stuck with it forever. I had a problem with the trans and had to pull it to replace the pump, when I saw the two rear galley plugs they were both wet. A simple test with an Allen wrench found both of them barely finger tight.
It looked like it leaked while running and just sitting as well. The new drivetrain is about 6 years old with about a hundred miles.