diagmaster software is to be used on common rail diag. If one knows what to look at, diagnosis can happen in minutes. Dealer only. Assumes that the tech(s) know what they're doing which is another subject in itself.
It is no longer a "it's got fuel why won't it run" like the old days, you loosen an injector pipe and if it squirts, it's got fuel. Things are completely different now. Just because you get fuel TO the pump, doesn't mean the pump is going to pump at the correct pressure and volume to supply the injectors; and the injectors themselves can "wear" and then bleed off so much fuel that it won't build pressure enough to actually run the engine. The SCV controls the supply pump and the SCV is controlled by ECU. There is no other "backyard" way of diagnosing, well, unless you want to throw parts at it. I do not suggest doing that. They're expensive parts.
in diagmaster, with a crank but no-start situation, run a datalog of the SCV current both actual and commanded, rail pressure sensor voltage and actual, and a few other things. With those, the diagnosis will be mostly clear. In order to properly diag, the tech needs to know what he's looking at and NEW techs don't; and sometimes the old guys dont either. They're still stuck on old-school mechanical injection and the newer stuff can be confusing. And...at the time I was messing with em, Kubota didn't have a very good system of comparing what the ECU is reporting vs what it "should" see on a known-good configuration, which complicated matters terribly for us.
I'm not in the business anymore but I do try to keep up with the entire industry. What I see much of is dealers that advertise their lowest shop labor rates to attract customers. I understand and respect that but we have to think about it. The lowest rates also mean they ain't paying the techs very well and that means higher turnover than should be and also a lack of GOOD help coming in. "Good" meaning experienced. You're not gonna pay a good experienced tech $20/hr and no commission because he ain't staying long when Deere up the street is paying more and better benefits and good commission pay on top of base rate. An experienced tech with a competitive commission is going to be $80-100,000/year, and charging $85/hr shop labor rate isn't gonna be enough to pay those guys. Been through it. Actually one of many reasons I am not in the business anymore. Refusal of C.O.L.A--prior COLA was in 2014 (I left in 2020). Very common within the industry. But with that, the other side of the counter....the business has to make money and the only way they can attract good help is with benefits and good pay, and that is gonna mean that the shop is gonna have to be somewhere around $140/hr, or whatever. It's an unfortunate snowball cycle.
Oh BTW the guy who tried to buy it from you likely has parts to make that tractor run, stashed in the toolbox.