Ok lets start from the beginning.
Any dealer that told you " It could be leaking at the injector pump", NEVER go to them for service because they are clearly idiots! Why do I say that, well you don't have an injection pump on that model.
You only have a supply pump and it works completely different than an injector pump, lets just say it's a high volume high pressure fuel pump, and the chances of that that type of pump leaking fuel into the oil would be extremely rare!
Ok first do yourself a huge favor and get the WSM for your tractor!
P/N 97897-13270
Next I'm going to say your problem is probably going to be in the connection from the lines on the common rail to the injectors.
For most they are used to seeing the injectors , and connections on there tractors, not on this model all the connections are hidden inside the valve cover.
Pull the valve cover and look at all the parts very closely, all it talks is one nick in a O-ring or a seal to cause a huge issue.
You could even reconnect the Injectors with the cover off and look for leaks.
Do not over tighten the injector lines as they are just an O-ring seal and over tightening them will just crush and destroy the O-ring.
Also note that the high pressure return also goes to the head and then back to the tank, so check every connection, and honestly wouldn't hurt to just put all new O-rings and gaskets in it while you have it open!
((4) #60) P/N 04814-05110
((5) #30) P/N 1C020-96730