Make sure that the o-rings aren't getting pinched. It doesn't take much to cause a little seepage.
I thought about something along those lines jus a dab around the lip of the push rod cover. I took them off and reseated one more time with the new rings...Check for any burrs where the O-ring seats. May try a some silicone gasket sealer. Just small amount, don't want it squeezing out inside engine.