My 400 BB was recently Rebuilt (500 miles). Oil pours out (behind Damper) after Engine is shut down. It can idle for 30 min. with no leak. I have heard of some problems with faulty timing chain covers manufactured with crank seal off centered. It didn't leak until recently 400+ miles. Oil pan and windage tray are new. I have retourked the pan bolts to make sure all is tight.