rScotty thanks for the compliment. You know more about these than probably anybody else posting here based on your decades of experience, your engineer's analytical approach, and your extensive original document collection. Did you say once that back in the day, you considered buying a Yanmar dealership?
I agree a year and a half isn't long for a diesel to sit unused. Idle time will deteriorate a battery, but I can't think of any other component harmed by time. The delicate stuff is protected by immersion in oil or diesel.
In the case of my YM240 I think it contained nothing but pre 1994 eye-burning high sulfur diesel when I bought it in 2003. I was told the tractor was started only a couple of times in the preceding decade. Then the short-time second owner I bought it from did more harm than good trying to remedy difficult starting. When I flushed and replaced the nasty fuel that made a night to day difference, it now started instantly and ran like new. My point here is that time unused hadn't hurt the tractor. (aside from the weathered appearance). All it wanted to run nice, was fuel that was up to spec.
(my later experiment with nearly 100% biodiesel was a detour into hard starting again, but I recognize that I caused that myself).
Others might know how long diesel lasts when it isn't used. My guess would be 5~10 years before it will give you problems if the filter bowl doesn't look clouded. I don't think this 2310 will have any problems at all.