I am not so sure it is "common" but I also don't know of any polls or surveys that indicate one way or the other. I believe most people just change their oil and filter according to the schedule and never do an analysis. But people on diesel forums are a different breed and there might be a higher percentage of them doing analysis. People who long haul tow for a living may also be a group that does oil samples. I used to do samples periodically on my 2003 because I wanted to run full synthetic at twice the mileage given in the schedule (which was for conventional oil) and wanted to determine if that was good. With my 2015, I am going by the schedule (so far) and changing my oil with far fewer miles on it so I have seen no need to do any samples and may never do one. If I did samples to check on the engine condition, I'm not sure what I would do differently if I got a bad result. I'd probably post my results here and fret over them.
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