Lots of potential oil leaks on these engines ask exactly where the leaks are. Valve cover gaskets front cam and or crankshaft oil seals leak, rear crank seal or the plate at the back of the flywheel (passenger case side of engine) all possible sources of leaks.
It could be just the valve cover gasket or an oil seal. These engines have problems with the head gaskets, but they are usually leaking coolant. Your mechanic should be able to tell you where is the leak exactly.