It is pretty easy to contaminate a sample if you are not really careful. One time someone in our outfit used one of the little bellows plastic pumps to pull some antifreeze out of a radiator. They washed it out with water and put it away. Next time we sampled oil it came back with antifreeze detected. Scratched our heads till we remembered what the previous use for the pump was.

I definitely would not tear an engine down based on only one report, without something else to back it up or pull another sample.

John