My money is on the oil filter. That was the issue with mine about 1 year ago after I took it to iffy ube. Very easy to check. Look down in between the radiator and the front of the car at the oil filter. You should be able to see oil on the Y pipe. If you are not sure, just tighten the oil filter.
Before you do that, make sure it is threaded in correctly. Yes, I am actually suggesting that you get a new oil filter and another quart of oil to put in.
+1 to that, swapped with OE and the problem went away. In fact I'm shocked at my oil level after ~9K KMS (change at ~10k int) as it hasn't moved!