Very good info. I am going to look at my 7.3 to see if the same problem is going on. Thank you.....Im assuming your truck has the 7.3? Its VERY VERY uncommon for a real main to go on these motors!! If you research it there is some tube that comes down the back of the motor and has oil that comes out of it. (its suppose to do this but it looks exactly like a rear mail leak) and MANY people confuse this for a rear mail leak. So just check into it. I would put money on it that it is not your rear main.. and anything that leaks into the valley of your motor will leak down there also making it look like a rear main.