Are the heads leaking
oil or water? is your
oil black or frothy brown looking? have you checked? do you notice
oil traces from the bottom of the head down the block? or is it leaking from the bottom of the valve cover gaskets down the head?
If it is any leaking other than from the valve cover gaskets you may try re-torqing the heads (sometimes works,usually doesn't work). Then you are faced with pulling the top-end off, replace the head gaskets ,manifold and exhausts and put it all back together again.