I'm not sure. I had the heads off in the winter, everything looked good in the cylinders, pistons. I did not re-ring it, but I am using a pvc valve on the right cover and a breather on the other. It leaked in the same spot last time around with my 906's. I put 915's on and still leaks same spot, that's why I thought maybe the cover was warped. Just gonna keep pullin my hair out...