We purchased a used 2012 Ford Explorer XLT back in April 2013 (19000 km). We brought it into the dealership last month for its check-up and the mechanic found oil in the coolant reservoir. After a few flushes and us returning with the same problem, they replaced the water pump and a few hoses and told us the problem was fixed. The memo says that after the job was done, they flushed the coolant again, took it for a test drive and there was no oil in the coolant. As a result, they told us the problem was fixed. The very next day I go get some groceries and check under the hood. Once again, oil in the coolant reservoir. It is not much...maybe a few millimeters but still obviously present. We took it back to the dealership and they are claiming that it is simply the remnants of oil from the leaking water pump and that it will never completely go away no matter how many times they flush the system. They are adamant that they have rectified the problem and that the remnants will do no harm to the future of the vehicle/engine performance. My question is whether this is true and we should accept that the 2 year old vehicle will always have oil in the coolant system until all the remnants burn off or whatnot or are they trying to not fix a bigger problem like the head gasket. I want to believe them but I find it difficult to believe that this will not affect the engine down the road. Any input would be great.