 If you're considering buying this car, please look into the N64 customer care program for this car. There are about 20 engine components that were essentially recalled. Depending on when, or if, your 550i went through this program will determine the number of components you may have had replaced. Initially, BMW changed out these components, one at a time and each time you had a check engine light come on the would replace the next most commonly malfunctioning part. Eventually, they started flat out replacing all the components since they would eventually fail (I believe due to the heat and pressure they are placed under with the twin turbo.  This added up to owners paying for their vehicle while they spent months in the shop. While BMW did cover the costs of the replacement and extend the warranty, having engine issue undoubtedly will lead to transmission issues. This was the case of the most recent 550i owner I met at an German auto shop while getting another vehicle pre purchase inspected. He said he spend over 10k on transmission work and eventual replacement while he owned the vehicle for only 6 months, 2 of those months was spent in the shop. These repair costs were not covered by BMW.   Some sleazy owners, will not mention this program/issue at all to you when selling the car (which was what happened in my case). Luckily the deal fell through in the 11th hour at the bank when the vehicle failed state inspection (due to worn out tires and brakes in this case). Owner claimed that both tires and brakes were replaced within the last 6 months. Some owners and used car salesmen are doing whatever they can to u load these problematic vehicles. Buyer beware!!!