I learned something new from a "brand x" friend that could work on our old Fords. He was trying to track down the source of an oil leak. He hooked a vacuum pump to the breather and plugged all the vents in the valve covers (front of the pan for most flatheads) and went around all the gaskets listening for a leak and probing with a feeler gauge. As he found the areas that could leak, using a tube of black gasket maker, let it suck the sealer in and in a short time had all (3) places it could leak sealed up.