I have a oil smell from my Renault Megane anyone know why ?

I have a 1.6VVT Renault Megane on a 2007 plate ,its only done just over 20k miles ,However we keep getting this smell of warm oil through the heater vents more so when we pull away from a Junction or move of from sitting still , its been in the dealers 6 times now and they have flushed the oil and did a oil change but its still doing it just the oil smell is newer , i cant see any leaks and the breathers have supposed to have been checked and have no clue , the car is going to be out of warranty soon and i am just wondering if the dealer is trying to fob me off untill then ,The car is on Finance and we have only had it a few months so we are going to reject it if they cant fix the problem this time ,its got a few other problem which they have been asked to address , the car is back at the dealers yet again , anyone have any ideas ?