You could have overworked your disc and glazed your flywheel. Some of the friction material kinda melts itself onto the flywheel's surface, making it semii-slick and hard to engage the disc. That happened to me once while I was semi-intoxicated. I though it would be fun to do some 3-4k clutch cumps on the street, and after about the third one, it didn't grab at all. I spun all the way thru 1st, 2nd, and 3rd. When I got home, I noticed that wonderful burnt clutch smell. It took about a week for it to go away, and the clutch seemed back to normal. I don't think oil from your main seal would be a factor, since the flywheel's rotation would probably spin off any oil that got onto it.