What is the best Oil to put in a 528I.

How old is your car? I ask this only because of the mileage involved. If your car has a lot of miles, meaning over 100,000, you might want to consider a heavy oil or something to that effect. Using the synthetic oil in your car would not help much because of how old your engine and how much mileage it has. If it has really low mileage, I strongly recommend using todays synthic oils and only those once you change to it.

How about extended gurantees? Mine is up or is going to be up and I want to extend it?