White smoke, excessive oil burning, burned oil traces on engine cover
 

Hi! I was hoping someone can help. I have a 2010 a6 3.0t supercharged bought about a month ago (private owner). The first time I've got the low oil pressure light I took it to the mechanic for an oil change and asked him to inspect it to see if there was a leak. He said he saw nothing. Mind you the car has high mileage. Now it has been less than a month since the oil change and the oil pressure light came back on indicating my oil is at its minimum. I noticed oil caked up on the engine cover so I immediately thought it could be a bad valve cover gasket. But since the oil light came back on I've also noticed whitish smoke coming out of the exhaust. It has been humid here the past couple of days so I can't tell if the smoke has a blue tint in it. Engine light is also on and it's throwing P0420 code. Could it be the breather valve diaphragm? Also coolant levels are the same. No overheating issues and the smoke only happens when the car is idling or comes to a stop. Thank you!