[slartyblarfast]

That kind of endplay has been know to happen. What happened is the thrust bearing surface has been damaged. It allows the crank to move and push out the seal. It's not common but has happened enough that I have seen 3 or 4 do it. If you are lucky you can get away with a crank kit. New crank, and bearings. Sounds like that's all you need. Do you have Powertrain warranty? If so it should be covered.