Since it smells like oil I'd suggest checking for a possible oil leak. They can start as a seep and spread across engine components before ever accumulating on the ground. Look closely as it might not have acquired into a drip yet. I'd suggest checking out our engine oil leak diagnosis thread to help you look over common oil leak areas to help you possibly pinpoint your issue:
http://www.pelicanparts.com/techarticles/MINI_R56/83-ENGINE-Oil_Leak_Diagnosis/83-ENGINE-Oil_Leak_Diagnosis.htm. Let me know what you find.