Hi everyone, I have a 2008 STS with a 3.6 and 52k on her.. This car is very well cared for and I have noticed since i got is last September that it has a light soot build up in the tail pipes.. The engine gets its oil changes, I havent noticed any performance issues and my daily driving is 25 miles to work each way at hiway speeds.. I dont think its a good sign... Anyone have any thoughts ?? Should I be concerned ??