This is what I am going thru right now with my 2009 CPO BMW 335d.
I purchased a CPO 2009 BMW 335d with 46,700 miles on it about three weeks ago from a BMW dealership about 80 miles from my house. The SERVICE ENGINE SOON light turned on the first week I had the car. Brought it over to my local BMW dealership and they replaced the mass air flow sensor. During the second week I had the car, the SES light turned on again, so I brought it over to the dealership thinking it was probably another sensor. After running tests on the car, they determined that the problem was CARBON BUILD-UP.
They told me that they ordered a new cylinder head, intake valves, and new injectors. When I asked the service rep to tell me what the hell is going on, he said that the injectors failed and leaked, causing sludge and build-up on the intake valves. He said that this was the first DIESEL 335d that he saw this happen to. So they received the new parts this week, but they were not assembled. The service rep to told me that they need to have the machine shop do some work on it and it will take one more week to complete everything.
So now it looks like they are rebuilding my engine. I am not a mechanical person, but doesn't seem a bit extreme with a car that only has about 47,000 miles on it. Just wanted to find out if anyone else had similar problems with their diesel engines.
After all is said and done, I will have a rebuilt engine. The service rep told me that the total cost of the work being done on my car is about $10,000. It's good that the car is CPO and comes with the extended warranty, but what if this happens again after the warranty runs out. There is no way I want to pay that much money to fix it.