I recently purchased a 2006 325I certified used BMW, the car was previously lady owned and driven. Only dealer serviced, so that means that with the 53xxx kms on the car the oil has been changed 2 maybe 3 times. When i looked under the oil cap it looks like sludge build up on it but inside the valve cover it looks fine (just a little brown). This bothers me but the dealer swears its perfectly normal, so my question is has anyone ever had their engine flushed? Should i be worried about this?