I have a 2009 R53 that needed its catalytic converter replaced. When the shop took it apart there was a large amount of hard buildup in the number one cylinder exhaust port at the head going to the exhaust manifold which was noted by the tech to be the reason the catalytic converter failed. The spark plug is not black or burnt up nor does it have any oil either. We had the cat replaced and took the car home for further investigation.
We are trying to figure out where the buildup is coming from if the spark plug is clean. The guys at the shop wanted another $2000 to do a head job that we can do ourselves once we find out what is really going on.
In my head, if the valve seal was leaking then the spark plug SHOULD be really ugly and black.
So I have attached some pictures here to see what I'm talking about and any advice/help would be greatly appreciated!




Catalytic Converter that was replaced.



Exhaust port from head going to manifold.

 

Going to move you to the Gen2 area.