You are describing a valve cover gasket that is leaking. This is a common ailment. Small amounts of oil can drip onto the exhaust manifold and this makes smoke. Sometimes the smoke is heavier than other times.
The oil that's coming out is not under pressure, so it isn't spraying out it is just dripping. Oil is pumped under pressure to the top of the motor where it then flows by gravity to the bottom and begins the journey over again. Your leak comes from oil that is pooling at the rear of the engine before it flows down through the many drain holes that take the oil to the oil pan.
You can have this leak for a very long time and not do any damage beyond getting serious oil stains on the side of the block/cylinder head, and the exhaust manifold. Eventually you will have oil stains on your garage floor.