[QUOTE=bmwoem1;7340307]The reason why these passages get clogged is due to leaking exhaust valve stem seals. The oil leaks down the back of the valve and eventually becomes carbonized due to the heat. The secondary air holes are right next to the exhaust valve guides. I've done this job many times (I'm a BMW tech)[/QUOTE I was wondering how the passages get clogged , Okay,,,,,,,so is the valve steam seal failure due to the 15,000 mi oil change intervals that bmw recomends....And also is the higher oil temperature on the 545 the reason for gasket and the seals leaking prematurely due to the higher temps breaking the oils protection ?? Due to bmw not equipting the 545 with an oil cooler ??