I came back from the shop. Spent $70 for a steam cleaning to clean out residue oil. On the same day, the car dripped oil at same amount. But it definately comes from top of oil dipstick and accumulates down around dipstick tube and drips on the floor. There is no appearant leak from low oil pan. The mechanic also found some minor leak in the left side of the engine.
I include the notes from the mechanic:
"Engine has oil coming out of top of dipstick. Problem could be clogged crankcase ventilation system or worn rings causing too much pressure. Will need to do leak down test to start."
The mechanic needs charge more to diagnose the problem further. If it's worn ring, basically the car will need a new engine. That will be lots of $$$$. I don't prepare to do that. But if it's clogged crankcase ventilation system, that can still be reasonable to get it fixed. But my quetsion will be: how likely this is the case? How can I determine it myself? If it is, how do I clean it up? Should I replace the PCV valve?
Any also I find some oil residue in the air filter.
Your input is greatly appreciated.