It must, i went as far to take the motor back out and it went back to the machine shop and after they checked the crank and the seal for fit up he said it should not leak. Put it back in and it still leaked then i proceeded to call indy where i got the rotating assembly from and they told me they all leak a little but since i run a 4spd it is a little hard on the clutch. So at that point i talked to my buddy that was a dodge tech and he starting asking around and found out about the anti leak rear main bearing dodge had to make to fix all the oil leaks in the late 80s early 90s when they quit making the 360s with knurls on the crank.So i installed the anti leak bearing and guess what no leaks. I am no machinest but i had no leaks with 3 other 340s with the knurls on the crank and the motors where all built by a very good machine shop and same shop. The knurls on the crank are cut in the crank in a way that it channals oil away from the seal.I have always used the felpro rubber seal.What seal are you using?