You might check the 4 rubber plugs in the head that seal the valve cover to head. Two in front and two in back. If these are not replaced when for example the valves are adjusted they will tend to leak. New valve cover gaskets do not contain these seals. See Bentley Fig. 4-33, 4-39, 4-40, etc. to locate. Then again might be an oil pan gasket or something simple like a loose oil filter. Have had the oil pressure sending unit leak quite a lot of oil too. Doubt you have a cracked block. They tend to leak coolant rather than oil out side the crankcase. You need to locate exactly where it is originating from first by cleaning the entire engine then search.