Hi Kamal, I did check the warranty booklet and it is a bit of a grey area with gasket, hence why they reject the warranty as it is not very clear and one could understands this part is under warranty but as it is not clearly stated they are using this as an excuse to reject it...
With regards to dealers, Mobilo took the car to the closest MB from my home, so I did not have a choice on this basis. To be fair MB in Colindale have done their best to assist on this occasion with my claim. When it comes to servicing my car like all previous mercedes cars I have had, I always go to mercedes in Milton Keynes, as they are really friendly and very good at servicing your car and looking after you as returning customer. From my experience, the service is much better than a Mercedes Benz in London and is cheaper too.