Was it a new bore?
or just a re-hone?
Did you check for out of round?
These larger bores can go out of round pretty easy.
These motors do have a lot of pumping within the crankcases, that is a big pistion going up & down with (comparatively) little crankcase volume to handle the pressure fluctuations.
I made my own crankcase breather system up to ensure the cases could breath easy.
If your breather isn't free enough, the back pressure on the rings can disrupt the seal