This is the key year for mainstream UK diesels because the N47 becomes the defining reliability risk on 318d and 320d models.
The rear-mounted N47 chain can stretch and snap, taking out the engine. Early units suffered from sharp crankshaft sprocket teeth (Recall 14V054). It is the key risk on mainstream 318d and 320d cars built in the late-2000s.
Petrol six-cylinders use an electric water pump that can fail with little warning, pushing the car into limp mode or overheating within minutes.
Twin-turbo 335i models suffer HPFP failures that cause long cranks, misfires under load, and limp mode, especially on cars that have been tuned hard.
Low voltage, jump starts, and age can corrupt the footwell module, leaving the car with lighting and window faults that can cause an MOT failure.