Six weeks ago I purchased an August 2008 BMW 520d Touring from a BMW main agent. It was supplied having being maintained from new by the same BMW dealer. When I bought the car, I noticed that the sump oil was slightly above the normal level. I questioned this with the supplying dealer, who had carried out a full pre-sale check of the car. As the level was about 5mm above the normal line on the dipstick, I was told not to worry.

I recently read a note by you about problems caused by fuel, not being burnt off from the particulate filter, ending up in the sump oil. The car's system tells me that the oil will need changing in 3600 miles. Should I have the oil changed now? What responsibility does the supplying dealer have if there is a problem with the engine? The car gets used principally on rural A-roads, with journeys of no less than 12 miles at a time.