Hello George,
Given that two independent measurements had confirmed there was a problem, suggests very strongly there is something to be resolved. The fact that the dealer now fails to find a problem , may be down to a number of factors.
You may well have seen other threads on the forum that explore the challenge of getting reliable moisture testing carried out.
There are a number of factors that affect the reliability of the reading.. just to mention a few of them, the instrument and its calibration status, the technique used to obtain the reading,
and given different weather/storage conditions the readings can change.
So it is quite possible for different readings to be obtained by two different people, and even more likely the reading will be different on different days.
The question is how different were the two sets of readings? If the first set were just above the threshold, and the second set just below, that could be normal variance due to some of the factors above. But if the readings were radically different then that calls into question one if not both sets of results.
In this situation the dealers first set of results confirmed your own engineers evidence, and that places a high probability there is a problem. So I should insist the rail is changed.
If the dealer is reluctant to change the rail then do contact the manufacture direct, tell them the details and supply copies of the reports, even if the first report was not done by a manufactures approved dealer, it is still evidence of a problem which was confirmed initially by the dealer. ask the manufacture to have the rail replaced.