The first step I would undertake is to thoroughly clean the engine. I am not sure where you are located but around here I would go to a self serve car wash and use the pressure wand to spray it all clean. Use an engine degreaser and apply it as well to the back of the engine and the top of the bell housing. You should also spray from the underside and clean of as much of the oil, grease and debris as you can get. Let the engine dry for a while. The perfect way would of course be a ramp or a hoist where you could look under the vehicle. Sometimes oil change stations can provide you with that as well. Anyhow ones your engine and undercarriage is clean you can let the engine run and see if you can isolate the source. It is most certainly possible that it is the valve cover gasket, as well as the rear main crankshaft seal or the pan gasket itself. Also, if you have an automatic transmission it may be leaking from the font of the transmission intake shaft. Unless you clean it, inspect it and isolate the leak, there are to many variables to positively identify your leak. Good luck