Oil leak can be attributed to several factors.
1. Gasket failure.
2. Uncontrolled Crank case pressure Failure.
Tighten both the valve cover and oil pan bolts.
Replace the Positive Crankcase Ventilation Valve and vacuum line.,
This is a valve causes a negative vacuum on the engine while its running, As to say if it had a leak in a valve cover it should not be leaking while its running, only when the engine it turned off.
The most common sign of a leaking rear main seal is oil spots on a driveway or garage floor where the vehicle is parked for long periods of time. Oil may leak from multiple areas of the engine, but the rear main seal is one of the most frequent sources of a leak.
Often leaking oil from a rear main seal will drip onto the vehicle's exhaust and cause smoke to come from under the car. Smoke coming out of the tailpipe is a sign that the engine is burning oil, not a leaking rear main seal.
Accumulation of Debris
Leaking oil acts as an adhesive on the bottom of the car. Dirt and other road debris will stick to surfaces covered with oil. An accumulation of dirt and other debris at the junction of the engine and transmission is a good indicator of a rear main seal oil leak.
Hope this tip guides you in the correct direction to solve this problem