Start by spraying degreaser all over the engine, top to bottom and underside. Scrub and spray off all oil and dirt deposits and let dry. Run the motor or go for a ride until you start seeing where the oil is seeping out. Most likely it's one of the gaskets. Look at the head gasket, the one that's in between the valve head and the top of the cylinders, that's the one that usually goes first. Also check out the breather tube, it's a long rubber hose that is connected to the cam cover, the top cover of the engine. It's usually connected to the back of the cover and runs down towards the ground. You may be spraying oil through there. Check the oil drain plug and oil filter mount. Figure out where the oil is leaking and we'll go from there.