Has the pcv valve ever been replaced on the motor ? On top of the intake manifold there is a small black cap with 2 bolts in it. You will need a needle nose pliers to pull it out to replace. When these get plugged up cause oil leaks all over the motor. A motor is like a air pump, when the pistons travel up an down builds pressure inside the block. When the pcv (positive crankcase venalation valve) gets stopped up, the internal pressure build up causing blew by thru gaskets an seals. I would replace this before starting any major work an see what happens. Cost about 5.00 for one which most people an place do not replace.