A little bit of useful knowledge on this issue.
I am having my car serviced in 20 days time and have an oil issue with my FR - it simply uses too much irrespective of driving style. So, I mentioned this to my dealer and we had the following dialogue
Me: My car is using a lot of oil on a monthly basis so perhaps its something you can address when the car is serviced.
Dealer: What type of oil are you buying?
M: Well I looked in the manual and I buy one of the four suggestions, VW501/502, etc
D: Ok but which brand?
M: Either Castrol GTX, or Mobil I think
D: Well you should be aware that you must use the correct oil supplier for your car - it should say it in detail in the manual or the filler-cap.
M: Oh, and if I dont?
D: If you dont, then should your car suffer any issues which can be directly related to the type of oil, e.g. engine component issues, the warranty will not cover you
M: Right, thats stupid.
D: I agree, but its the guidelines we have to follow.
The above is a true conversation - I decided to type it out when on the phone so I had record of it. Its shocking, and I will think twice before buying any other brand of oil.
M