I have owned my audi since October, it is the 1.8 TFSI model. The oil was last changed by Audi in the service at 27k miles, that was in February. Today the oil low light came on, I guess I only need to top it up but I would like to buy the same oil that was used in the service. Am I right to get Castrol (as the oil cap is branded) or is it not a good idea to just top it up? I didn't want to mix two types of oil but equally I don't want to change the oil now if a service is coming up. I don't know what my service schedule is, I am just waiting for the indicator to tell me to have it done as I was led to believe that's how it works on these cars.