I think i know what your problem is. Are the new valve covers aluminum, finned, polished and no name brand? Did you buy them off ebay or at. Swap meet? If so...they are chinese knock offs ..the breathers are crap. They have an oring in side that does not seal. The pcv is probably inside the breather. What happens is, oil is pulled up into the breather because there is either no baffle inside the v/c or the one in the cover is a pos...oil puddles inside the breather,after shut thev car off,wait ten minutes and oil runs out of the bottom of the breather. Couple things that can be done...seal the breather so no oil can come out of the bottom,put a restrictor inside the pcv hose...or just save up and buy some usa made breathers/valve covers.