I would figure you'd see oil only coming from the driver's side of the pan area or the flexplate cover if the rear main seal was shot...I had a bad real main...and my oil pressure pretty much sucked LOL
I'd wipe it clean...or as well as possible...and then start it and crawl under it...maybe you'll be able to see a visible leak spot...or paint the pan white around the edges...did that on my buddys car to pinpoint it...kinda lame, but it works.