Well when built new engine, being fully forged, tolerances were done a little looser for expansion, which created extra bypass pressure under boost which in turn push oil out rear main. To fix at the time I drilled out pcv hole bigger to let more air out which worked, but this created another problem of pushing excess oil through pcv system & back into intake, so decided to sort once & for all by putting new rocker cover on & adding this:
http://petersonfluid.carshopinc.com/.../43606/08-0450
now all sorted, relieves any pressure above 3-5 psi, have lighter spring coming just in case.